GB2475920A

GB2475920A - Safety and monitoring system for oil-fired boiler installations

Info

Publication number: GB2475920A
Application number: GB0921391A
Authority: GB
Inventors: Philip Rex Henderson
Original assignee: Haven Ltd
Current assignee: Haven Ltd
Priority date: 2009-12-07
Filing date: 2009-12-07
Publication date: 2011-06-08
Also published as: GB0921391D0

Abstract

A safety and monitoring system, especially for an oil fired boiler installation, comprising a valve unit 22 for fitting in a feed path 24, 26 from an oil storage tank 16 to a boiler 14, a boiler temperature sensor unit 28 and a remote unit 70. The valve unit shuts off the flow of oil from the tank to the boiler when the temperature measured by the senor unit exceeds a predetermined value. The valve unit also includes a pressure sensor for determining the pressure of oil in the feed path and a transmitter for transmitting a wireless signal dependent on the sensed pressure which is received by the remote unit where an indication is provided. Also described is a method of calibrating the system and a shape calibration which depends on the shape of the tank so that the indication provided by the remote sensor shows the volume of fuel in the tank.

Description

TITLE

Safety and monitoring systems for oil-fired boiler installations

DESCRIPTION

This invention relates to oil-fired boiler installations for buildings and in particular to a safety and monitoring system for use in such an installation.

It is customary for an oil-fired boiler to be situated indoors so as to protect it from the elements. It is also customary, and indeed a requirement of regulations in some jurisdictions, for the boiler's oil storage tank to be situated outdoors and for a fire safety-valve to be fitted outdoors in the feed path from the tank to the boiler. The valve is normally open, but is triggered to close by a temperature sensor disposed in or adjacent the boiler housing when the sensed temperature exceeds a preset value. In the case of overheating of the boiler by itself or as a result of fire spreading from elsewhere, the supply of oil is cut off.

It is useful for a householder to know when the level of oil in the storage tank is becoming low so that they can order a delivery of more oil before the tank runs out. The level can be checked by a sight-pipe alongside the tank, if one is provided, or by a dipstick, but this requires the householder to go to the tank. To avoid the need for this, remote level sensors are known. One example, sold under the trade mark Watchmansonic, has a sender unit which needs to be fitted to a hole formed in the top of the tank at the same level as the fill point. The sender unit determines the depth of air between the sender unit and the oil surface from the time of flight of a sound wave reflected by the oil surface, and transmits the distance as a radio signal.

A remote receiver unit, which may be located in the house, is calibrated with the depth of the tank using an 6-bit DIP switch, receives the radio signal, calculates the depth-wise fullness of the tank by subtracting the air depth from the tank depth and dividing the difference by the tank depth, and displays an indication of the depth-wise fullness. A problem with this remote sensor system is that it requires a hole to be formed in the tank at a particular level. It may instead be possible to form the hole more easily in the cover for the fill point, but then the sender unit would be disturbed and possibly damaged each time the tank is filled. A further problem with this system is that it needs to be calibrated using a 6-bit DIP switch and a decimal to binary look-up table. Yet another problem is that although the system provides an indication of depth-wise fullness of the tank, it does not indicate volume-wise fullness of the tank unless the tank has a constant area at all horizontal cross-sections.

An aim of the present invention, or at least of some embodiments of it, is to overcome at least some of the problems described above.

In accordance with the present invention, there is provided a safety and monitoring system for an oil-fired boiler installation having an oil tank connected by a feed path to an oil-fired boiler. The system comprises a valve unit for fitting in the feed path from the tank to the boiler, a sensor unit for fitting in or adjacent the boiler and operable to sense temperature, and a remote unit. As is known, the valve unit includes a valve which is responsive to the sensor unit for shutting off the flow of oil from the tank to the boiler when the sensed temperature exceeds a predetermined value. However, the valve unit also includes a pressure sensor for sensing the pressure of oil in the feed path, and a transmitter for transmitting a wireless signal (such as a radio signal) dependent on the sensed pressure. The remote unit includes a receiver for receiving the wireless signal, and an indicator for providing an indication dependent on the sensed pressure. In a typical installation for a building such as a house, the oil tank and valve unit would be disposed outside the building, and the boiler would be disposed inside the building but in an out-of-the-way place such as a boiler room, scullery or garage, but the remote unit would be disposed inside the house, within range of the transmitter, in a place where the remote unit is readily accessible and noticeable, for example in a hallway or kitchen. From the indication provided, a user can determine, for example, whether they need to arrange for the tank to be topped-up. By forming the valve, pressure sensor and transmitter as a single unit, the installation of the system is straightforward, and indeed in many cases a conventional fire safety valve can readily be replaced by the valve unit of the invention. With the system of the invention, there is no need to form an additional hole in the oil tank.

The pressure sensor is preferably arranged to sense the pressure of oil in the feed path upstream of the valve so that closure of the valve does not substantially affect the indication which is provided. If the oil feed path includes a pump, the valve unit is preferably fitted upstream of the pump, so that operation of the pump does not substantially affect the indication which is provided.

In a simple embodiment of the invention, the indication that is provided may merely be the value of the sensed pressure. However, this requires the householder to remember or make a note of the pressure at which the tank needs topping up, especially if the tank outlet is at a significant height above the pressure sensor. Alternatively, the indication that is provided may be whether or not the pressure is below a preset value. However, this may not give sufficient warning of the need to top up the tank when the weather is very cold and the oil consumption rate is very high, or it may give a premature warning when the oil consumption rate is low.

Also, the amount of oil in the tank is dependent not only on the sensed pressure but also upon the density of the oil.

In a first preferred embodiment of the invention, the system has the ability to be calibrated with a density calibration according to the density of the oil and to apply the density calibration to the sensed pressure so that the indication is dependent upon the head of oil at the pressure sensor. If the pressure sensor is at the same height as the bottom of the tank, the head of oil is therefore equal to the depth of oil in the tank, and an indication of depth is more useful to the householder than an indication of pressure. Particularly if the pressure sensor is not at the same height as the bottom of the tank, the system preferably also has the ability to be calibrated with a height calibration according to the height of a first level in the tank (such as the bottom of the tank relative to the pressure sensor) and to apply the height calibration to the sensed pressure so that the indication is dependent on the level of oil in the tank relative to the first level, such as the bottom of the tank, in which case the indication is of the depth of oil in the tank, regardless of any difference in height between the bottom of the tank and the pressure sensor. The system preferably furthermore has the ability to be calibrated with a second height calibration according to the height of a second level at or adjacent the top of the tank relative to the pressure sensor, and to apply the second height calibration to the sensed pressure so that the indication is dependent on the fullness of the tank depth-wise, for example ranging from 0% of full depth to 100% of full depth. The heights of the top and bottom of the tank can be obtained by direct measurement and the measurements can be input to the system through a user input interface.

A problem with the first preferred embodiment of the invention is that it is reliant on density calibration. However, the density of the oil may not be readily known. Also, with its more preferred features, it is necessary to take height measurements and to calibrate the system accordingly.

In order to avoid the need for density and height calibrations, in a second preferred embodiment, the system has the ability to be calibrated with an empty calibration pressure for the pressure of oil when the tank is substantially empty and a full calibration pressure for the pressure of oil when the tank is substantially full and to apply the calibration pressures to the sensed pressure so that the indication is dependent on the fullness of the tank depth-wise, for example ranging from 0% of full depth to 100% of full depth. The system preferably has the ability to store a value dependent on the sensed pressure when the tank is substantially empty for use as the empty calibration pressure and for store a value dependent on the sensed pressure when the tank is substantially full for use as the full calibration pressure. The system can therefore simply be calibrated, for example by pressing a button switch when the tank is empty and by pressing another button switch when the tank is full, without the need to set multi-bit DIP switches or the like.

The first and second preferred embodiments can give an indication of the fullness of the tank depth-wise. For a cuboidal tank with vertical sides, the fullness of the tank depth-wise is equal to the fullness of the tank volume-wise. However, as will be discussed in more detail later, for other shapes of tank such as cylindrical (with a horizontal axis), spherical or an indented cuboid, the equality does not hold. For example, a spherical tank which is 5% full depth-wise is only about 0.7% full volume-wise. It is the fullness of the tank volume-wise which is of greater interest to the householder.

In order to deal with this, the system preferably has the ability to be calibrated with a shape calibration according to the shape of the tank (for example selected from a few basic tank shapes) and to apply the shape calibration to the sensed pressure so that the indication is dependent on the fullness of the tank volume-wise.

However the fullness of the tank is determined, the system preferably has the ability to determine when the fullness of the tank is less than a predetermined amount and to raise an alarm when it is, for example by activating a buzzer. The system can therefore attract the householder's attention when the tank is in need of topping up. Also, the system preferably has the ability to determine when the fullness of the tank is greater than a predetermined amount and to raise an alarm when it is. The system can therefore attract the attention of the householder or a deliveryman when the tank is being topped up and is about to overflow.

Specific embodiments of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of an oil-fired boiler installation in a house; Figure 2 is a partly-sectioned side view of a feed unit and sensor unit used in the installation of Figure 1; Figure 3 is a block diagram to illustrate the operation of the feed unit and sensor unit of Figure 2; Figure 4 is a block diagram to illustrate the operation of a remote unit of the installation of Figure 1; Figure 5 is a front view of one example of remote unit; Figure 6 is a front view of another example of remote unit; Figures 7A-D are isometric diagrams of four different basic shapes of oil storage tanks that may be used in the installation of Figure 1; Figure 8 is a graph showing, for each of the four tanks of Figures 7A-D, the volume-wise fullness of the tank as a function of its depth-wise fullness; and Figure 9 is a graph showing, for each of the four tanks of Figures 7A-D, the difference between the volume-wise fullness and depth-wise fullness of the tank as a function of its depth-wise fullness.

Referring to Figure 1 of the drawings, a house 10 has a boiler room 12 containing an oil-fired boiler 14 fed with oil from a storage tank 16 situated outside the house 10. The tank has an isolating valve 17 at its outlet. The boiler 14 is also supplied with electricity from a mains outlet 18 to power its control system which can be set by user controls 20. Referring also to Figures 2 and 3, a fire safety valve 22 is situated outside the house 10 between a feed pipe 24 from the tank 16 to the valve 22 and a feed pipe 26 from the valve 22 to the boiler 14. The valve 22 is responsive to a temperature sensor 28 disposed either in the cabinet of the boiler 14 or immediately above it. The sensor 28 is in the form of a phial 30 connected by a capillary tube 32 to a bellows 34 in the valve 22. The phial 30, tube 32 and bellows 34 contain a gas at sub-atmospheric pressure. The valve 22 has a valve body 36 containing a valve member 38 in a passageway between an inlet port 40 and an outlet port 42 of the valve 22. The valve member 38 is urged towards its closed position by a spring 44, but is normally held in its open position by a mechanical latch 46. When the temperature of the phial 30 of the sensor 28 increases, the gas expands causing the bellows 34 to expand. Once the phial 30 reaches a predetermined temperature (such as 65 or 90 Celsius), the bellows 34 has expanded sufficiently to release the latch 46, whereupon the spring 44 forces the valve member 38 to close and shut off the supply of oil to the boiler 14. Once the temperature of the phial 30 has decreased sufficiently, a reset button 48 may be manually operated so as to return the valve member 38 to its open position where it is again held by the latch 46. The reset button 48 may also be manually operated when the valve member 38 is in its open position so as to release the latch 46 and check that the valve member 38 moves properly to its closed position. The bellows 34, spring 44 and latch 46 are contained in a housing 49 mounted on the valve body 36 over the valve member 38 and reset button 48. As described in this paragraph, the fire safety valve 22 and its operation are conventional, and may be provided by a "KBB" fire valve which has been marketed for many years by Teddington Appliance Controls Limited, of St Austell, PL23 3HG, United Kingdom.

In accordance with the embodiment of the invention, the conventional KBB valve is modified as will now be described.

The valve body 36 is formed with a pressure port 50 between the inlet port 40 and the valve member 38 which applies the pressure of the oil at the inlet port 40 to a pressure sensor 52. The pressure sensor 52 may be of any suitable type which produces an electrical analogue or digital output signal dependent, and preferably linearly dependent, upon the applied pressure, preferably in a range from 0 to 100 kPa gauge (0 to 1 bar). The pressure signal is supplied to an encoder 54 which encodes the sensed pressure in a short range radio signal generated by a radio transmitter circuit 56 and radiated by an antenna 58. The transmitter circuit 56, encoder 54 and, if need be, the pressure sensor 52 are powered by a battery 60. The pressure sensor 52, encoder 54, transmitter 56, antenna 58 and regulator circuit 60 are contained in a housing 68 mounted on the valve body 36 over the pressure port 50.

Referring now to Figures 1 and 4, the installation also includes a remote unit 70 which is plugged into a mains outlet 72 in any convenient place in the house 10. Referring in particular to Figure 4, the remote unit 70 has a housing 74 from which a set of plug terminals 76 project for insertion into the mains outlet 72. The terminals 76 are connected to step-down, rectification and regulation circuit 78 which produces low-voltage DC electricity for powering other components of the remote unit 70. The remote unit includes an antenna 80 and radio receiver circuit 82 tuned to the broadcast of the transmitter 56, and a decoder 84 which decodes the received signal and provides a signal to a microprocessor 86 indicative of the pressure at the inlet port 40 of the valve body 36. The microprocessor 86 may have associated memory 88, which may include non-volatile memory used to store an operating program of the microprocessor 86 and parameters set by the manufacturer and/or user, and volatile memory used as working memory by the microprocessor 86. The processor 86 drives a display 90 which may take various forms such as a bargraph (or lightbar) display, a character display or a graphical display. The remote unit 70 may also include a buzzer 92 which can be activated by the microprocessor 86 and a user input interface 94, for example in the form of one or more push-button switches with which the user can control the remote unit 70 and/or one or more arrays of DIP switches with which the user or installer can set various parameters used by the remote unit 70.

In a first example of operation of the remote unit 70, the microprocessor 86 is programmed to cause the display 90 to indicate the pressure indicated by the pressure signal received from the decoder 84. For example, the display 90 may be a character display which indicates in characters the pressure in kiloPascals. Alternatively, the display 90 may be a bargraph display having twenty segments, and one segment may be illuminated for every 5 kPa of pressure.

One problem with this relatively simple first example is that the user is likely to be more interested in the degree of fullness of the tank 16, rather than the hydrostatic pressure at the inlet to the valve 22. Another problem is that, if the valve 22 is significantly lower than the outlet from the tank 16, the sensed pressure when the tank 16 is empty will be non-zero. A further problem is that the head H of oil above the inlet to the valve 22 is dependent not only on the pressure P but also on the density p of the oil in accordance with the formula H = P/(pg), where g is the acceleration due to gravity. For example, paraffin fuel oil or kerosene may have a significantly different density to diesel fuel oil.

In a second example of operation of the remote unit 70, which deals with the problems discussed above, the user input interface 94 includes three arrays 96,98,100 of DIP switches, as shown in Figure 5, by which the user or installer can set the density p of the fuel oil being used by the installation, the head 11mm when the tank 16 is empty and the head Hmax when the tank 16 is full. For example, the empty and full heads 11mm, Hmax may each be set by a respective 7-bit DIP switch 96,98 to indicate a head between 0 m and 12.7 m in 100 mm steps depending on measurements taken as shown in Figure 1. Also, the oil density p may be set by a 2-bit DIP switch 100 to indicate one of four densities from 800 to 950 kg/m3 in 50 kg/m3 steps dependent on the specification provided by the oil supplier or a measurement taken. The microprocessor 86 is then programmed by code in the memory 88 to calculate the depth-wise fullness D of the tank 16 from the formula D = { P/(pg)I -11mm} / { Hmax -11mm} where the depth-wise fullness D ranges from zero for an empty tank to unity for a full tank, and to illuminate a number of segments 102 of the bargraph display 90 in dependence upon the depth-wise fullness D in steps of 0.05.

In a third example of operation of the remote unit 70, which deals with the problems discussed in relation to the first example, the user input interface 94 includes two recessed push-button switches 106,108, as shown in Figure 6. With the tank 16 empty to its outlet, the user or installer presses one of the pushbutton switches 106, and in response the microprocessor 86 is programmed to store in the non-volatile memory 88 the current pressure as Pmm. Then the tank 16 is filled, and the user or installer presses the other of the pushbutton switches 108. In response the microprocessor 86 is programmed to store in the non-volatile memory 88 the current pressure as Pmax. During normal operation, the microprocessor 86 is programmed by code in the memory 88 to calculate the depth-wise fullness F of the tank 16 from the formula D = (P-Prnin)/(Prnax-Pmin).

The depth-wise fullness D is then displayed by the bargraph display 90 similarly to the second example described above.

For a cuboidal tank 16A, as shown in Figure 7A, with its four sides vertical, the volume-wise fullness of the tank 16A is equal to the depth-wise fullness of the tank 16A, as shown by the straight lines 109A, lilA in the graphs of Figures 8 and 9. However, for other shapes of tank, that relationship does not necessarily hold. For example, a right-circularly-cylindrical tank 16B, as shown in Figure 7B, with its axis horizontal, has a relationship between volume-wise and depth-wise fullnesses as shown by the curve 1 09B in Figure 8. The volume-wise and depth-wise fullnesses of the tank 16B are equal only when the tank 16B is empty, full, or half-full, as indicated by the curve 11 lB in Figure 9 showing the difference between volume-wise and depth-wise fullnesses. Oil storage tanks are commonly shaped generally as a cuboid, but with indented sides. Figure 7C shows a simplistic example of such a tank 16C with two indents 110 occupying the middle third of the height of the tank 16C and the second fifth and fourth fifth of the length of the tank 1 6C. The relationship between volume-wise and depth-wise fullnesses for the tank 16C shown by the three conjoined lines 109C in Figure 8, and the difference between volume-wise and depth-wise fullnesses is shown by the three conjoined lines 111 C in Figure 9. It will noted that the difference for the indented-cuboidal tank 1 6C is opposite in sign to the difference for the cylindrical tank 16B. Furthermore, if, as is shown in Figure 7D, the tank 16D is spherical, the relationships are as are shown by the curves 109D, 11 1D in Figures 8 and 9, respectively, which are exaggerated forms of the curves for the cylindrical tank 1 6B. The difference between depth-wise and volume-wise fullness can be significant, especially when the cylindrical tank 16B, and more especially when the spherical tank 16D are nearly empty. For example, when the depth-wise fullness of the spherical tank 16D is 0.05 (i.e. 5%), the volume-wise fullness is only about 0.007 (i.e. less than 1 %).

In order to deal with the problem described above with non-cuboidal tanks, the memory 88 may be used to store, for each of the three non-cuboidal basic shapes of tank shown in Figures 7B-D, data for transforming the depth-wise fullness D discussed in the second and third examples above to volume-wise fullness V. Also the user input interface 94 may include a 2-bit DIP switch 112, as shown in Figure 6, which the user or installer can use to set which of the four basic shapes of tank 16A-D is being employed. The microprocessor 86 can determine, from the stored data and the setting of the DIP switch 112, a volume-wise fullness value V which is then displayed by the display 90. The tranformation data may be provided for example as a set of three look-up tables representing the curves shown in Figure 6 or as parameters of a mathematical formula which is applied by the microprocessor 86 to the depth-wise fullness value D in order to calculate the volume-wise fullness value V. In a development to the examples described above, the microprocessor 86 is programmed to activate the buzzer 92 when the fullness value D or V falls below a preset value, such as 0.1 (i.e. 10% full), and the user input interface 94 may have a press-button switch 114, as shown in Figure 6, in response to operation of which the microprocessor 86 deactivates the buzzer 92. This feature can be used to alert the user that the tank 16 is in need of topping up.

Also, the microprocessor 86 may be programmed to activate the buzzer 92 when the fullness value D or V rises above a preset value, such as 0.9 (i.e. 90% full), and to deactivate the buzzer 92 in response to operation of the press-button switch 114. This feature can be used when the tank 16 is being topped up to alert the user or deliveryman that the tank 16 is almost full. Also, a further remote unit may be provided, for example carried by the deliveryman or mounted in his vehicle, which raises an alarm when the fullness value D or V rises above a preset value.

The microprocessor 86 may also be programmed to calculate, from changes in the fullness value D or V over time, the flow rate of oil and to raise an alarm when the flow rate exceed a preset value greater than the maximum flow rate during normal operation. The alarm will therefore be raised if there is a significant leak of oil downstream of the valve 22.

Although the embodiment of the invention has been described as being applied to the KBB fire safety valve marketed by Teddington Appliance Controls Limited, it may also be applied to other forms of fire safety valve, such as the KBB/E valve marketed by the same company. In the case of the KBB/E valve, the temperature sensor 28 provides an electrical output to the valve 22, where electrical circuitry in the valve 22 controls the valve member 38 using a spring-loaded solenoid. When the invention is applied to the KBB/E valve, the valve operating circuitry and the pressure sensing and transmitting circuitry 52-58 may employ a common mains adapter 64 and power regulator 60. Also, the temperature signal from the -10 -temperature sensor 28 may additionally be encoded by the encoder 54 and transmitted to the remote unit 70, where not only the fullness D or V of the tank 16 but also the temperature of the boiler 14 may be displayed.

It will be appreciated that many modifications and developments may be made to the embodiments of the invention described above. For example, the processing of the pressure signal may be performed at the valve 22, rather than by the remote unit 70, and the fullness value D or V may be transmitted by radio to the remote unit.

It should be noted that the embodiments of the invention has been described above purely by way of example and that many other modifications and developments may be made thereto within the scope of the present invention.

Claims

-11 -CLAIMS1. A safety and monitoring system for an oil-fired boiler installation having an oil tank connected by a feed path to an oil-fired boiler, the system comprising: a valve unit for fitting in the feed path from the tank to the boiler; a sensor unit for fitting in or adjacent the boiler and operable to sense temperature; and a remote unit; wherein: the valve unit includes: a valve which is responsive to the sensor unit for shutting off the flow of oil from the tank to the boiler when the sensed temperature exceeds a predetermined value; a pressure sensor for sensing the pressure of oil in the feed path; and a transmitter for transmitting a wireless signal dependent on the sensed pressure; and the remote unit includes: a receiver for receiving the wireless signal; and an indicator for providing an indication dependent on the sensed pressure.
2. An oil-fired boiler installation for a building, the installation comprising: an oil tank disposed outside the building; an oil-fired boiler disposed inside the building and connected by a feed path to the tank; and a safety and monitoring system as claimed in claim 1; wherein: the valve unit is disposed outside the building and fitted in the feed path from the tank to the boiler; and the sensor unit is fitting in or adjacent the boiler.
3. An installation as claimed in claim 2, wherein the pressure sensor is arrange to sense the pressure of oil in the feed path upstream of the valve.
4. An installation as claimed in claim 2 or 3, wherein the installation is devoid of any feed pump in the feed path upstream of the pressure sensor.
5. A system or installation as claimed in any preceding claim, further including means for calibrating the system with a density calibration according to the density of the oil and applying the density calibration to the sensed pressure so that the indication is dependent upon the head of oil at the pressure sensor.

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6. A system or installation as claimed in claim 5, further including means for calibrating the system with a height calibration according to the height of a first level in the tank and applying the height calibration to the sensed pressure so that the indication is dependent on the level of oil in the tank relative to the first level.
7. A system or installation as claimed in claim 6, wherein the first level is at or adjacent the bottom of the tank, and further including means for calibrating the system with a second height calibration according to the height of a second level at or adjacent the top of the tank and applying the second height calibration to the sensed pressure so that the indication is dependent on the fullness of the tank depth-wise.
8. A system or installation as claimed in any of claims 1 to 4, further including means for calibrating the system with an empty calibration pressure for the pressure of oil when the tank is substantially empty and a full calibration pressure for the pressure of oil when the tank is substantially full and applying the calibration pressures to the sensed pressure so that the indication is dependent on the fullness of the tank depth-wise.
9. A system or installation as claimed in claim 8, further including means for storing a value dependent on the sensed pressure when the tank is substantially empty for use as the empty calibration pressure and for storing a value dependent on the sensed pressure when the tank is substantially full for use as the full calibration pressure.
10. A system or installation as claimed in any of claims 7 to 9, further including means for calibrating the system with a shape calibration according to the shape of the tank and applying the shape calibration to the sensed pressure so that the indication is dependent on the fullness of the tank volume-wise.
11. A system or installation as claimed in any of claims 7 to 10, further including means for determining when the fullness of the tank is less than a predetermined amount and raising an alarm when it is.
12. A system or installation as claimed in any of claims 7 to 11, further including means for determining when the fullness of the tank is greater than a predetermined amount and raising an alarm when it is.
13. A safety and monitoring system for an oil-fired boiler installation, substantially as described with reference to the drawings.

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14. An oil-fired boiler installation for a building, substantially as described with reference to the drawings.
15. A method of calibration of an installation as claimed in claim 7, or any of claims 10 to 12 when dependent on claim 7, comprising the steps of: measuring the height of a lower level of the tank above the pressure sensor; measuring the height of an upper level of the tank above the pressure sensor; and providing an indication of the measured heights to the calibration means.
16. A method of calibration of an installation as claimed in claim 9, or any of claims 10 to 12 when dependent on claim 9, comprising the steps of: indicating to the system that the tank is substantially empty, whereupon the storing means stores a value dependent on the currently sensed pressure for use as the empty calibration pressure; and indicating to the system that the tank is substantially full, whereupon the storing means stores a value dependent on the currently sensed pressure for use as the full calibration pressure.
17. A method of calibration of an oil-fired boiler installation for a building, substantially as described with reference to the drawings.