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Boiler Fault Finder

Spark electrode(s)

Spark electrode(s) Reasons spark electrode(s) will fail to start: Cracked ceramic insulation (causing leakage) Poor terminal connections Incorrect spark gap between electrode(s) or between electrode and burner/target Electrode tip damaged / corroded / eroded Damaged ignition leads Bur
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Cylinder thermostats

Cylinder thermostats Reasons a cylinder thermostat will fail to start: Poor terminal connections Switch contact faulty Faulty timer/programmer When the timer/programmer is on, it sends a signal to the cylinder thermostat (this should then be live on the common terminal of the cylinder
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Room thermostats

Room thermostats Reasons a room thermostat will fail to start: Poor terminal connections Switch contact faulty Faulty timer/programmer When the timer/programmer is on, it sends a signal to the room thermostat (this should then be live on the common terminal of the room thermostat). Th
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Diverter valves

Diverter valves Reasons a diverter valve will fail to move: Wax capsule faulty Bobbin assembly faulty Faulty motorised valve head Seized push rod Contaminated system water / blockages (magnetite) Faulty pump Faulty primary flow switch and / or microswitch Faulty printed circuit board
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Motorised valve heads (diverter valves)

Motorised valve heads (diverter valves) Reasons a motorised valve head will fail to start: Motorised valve head lead faulty Burnt out motor windings Motor axle/spindle seized Faulty printed circuit board These devices are energised or de energised (via the printed circuit board) to op
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S Plan (HW zone valve and HTG zone valve)

S plan (HW zone valve and HTG zone valve) Suspect the zone valve as being faulty if the valve does not operate after the following checks: Electrically isolate mains supply and remove fuse – always check a 3 amp fuse is fitted Remove junction box cover Ensure there is no…
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Y Plan (3 port mid-position valve)

Y Plan (3 port mid-position valve) Suspect the mid-position valve as being faulty if the valve does not operate after the following checks (in order): Heating mode: Electrically isolate mains supply and remove fuse – always check a 3 amp fuse is fitted Remove junction box cover
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Synchronous motors (within zone valves)

Synchronous motors (within zone valves) These small motors are powered by 240V AC to rotate a spring loaded gearing arrangement, which in turn, rotates the spindle to open / close the valve. The motor windings can overheat and break, which is a common fault when motorised valves fail
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Actuator Heads (motorised valves)

Actuators (motorised valves) Reasons an actuator will fail to operate: Burnt out synchronous motor windings Valves spindle seized /sludge contamination Auxiliary switch (end switch) burnt out Gearing worn out Loose mountings Poor terminal connection These devices are energised or de e
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Solenoids & Moduregs

Solenoids Reasons a solenoid will fail to operate: Burnt out coil Poor terminal connection Loose mountings Armature sticking (Foreign matter accumulation jamming the armature) Faulty printed circuit board These electromagnetic devices are utilised to control the on/off/flow of gas thr
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Low water pressure switches

Low water pressure switches Reasons a low water pressure switch will fail to start: Damaged / loose wiring harness Switch contact faulty Blocked hole (sludge deposits) Calibration of switch faulty Air trapped within switch The low water pressure switch receives 230V AC from the printe
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Domestic hot water and primary micro switches

Domestic hot water and primary micro switches Reasons a domestic hot water and primary micro switch will fail to start: Switch contact faulty Damaged / loose wiring harness To test a domestic hot water and primary micro switch (on a demand): Electrically isolate boiler / system contro
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Primary Water Flow Switches

Primary water flow switches Reasons a primary water flow switch will fail to start: Punctured / perished rubber diaphragm Seized bearing plate spindle / out of alignment Damaged / loose wiring harness Switch contact faulty A demand for central heating will activate the pump and a rubb
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Domestic Hot Water Flow Switches

Domestic hot water flow switches Reasons a domestic hot water flow switch will fail to operate: Switch contact faulty Internal paddle / turbine / wheel not free moving (stiff/seized/reversed water flow) Punctured / perished rubber diaphragm Blocked pressure differential sensing pipes
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How to test boiler air pressure switches - boiler fault finder

Air Pressure Switches (Testing)

Testing the boilers Air Pressure Switch, is always an indicator that other problems may exist. This article helps to diagnose the Air Pressure Switch issues on a boiler.
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Air Pressure Switches (General)

Air pressure switches (operating @ approx. 0.5 – 4 m/bar pressures) See also: How to test your Air Pressure Switch with a multimeter Reasons an air pressure switch will fail to start: Loose electrical connections Kinked or split rubber hoses / loose hose connections Condensation withi
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Air Pressure Switches

Air Pressure Switches was last modified: October 27th, 2014 by Boiler Fault Finder
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Thermostats

… This content is for Annual Subscription and Annual Subscription Special members only. Please login to view this content. (or Register here.)Thermostats was last modified: May 15th, 2014 by Boiler Fault Finder
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Thermostats – Over heat Cut Out

Over heat cut out thermostat (Set @ approx. 90 – 98 degrees C) Reasons to activate an over heat cut out thermostat Scale / magnetite deposits causing excessive heat build up Loss of system water Loss in manufacturers calibration Faulty pump or pump speed too low Too much air within&he
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Thermostats – Liquid Expansion

Thermostats – liquid expansion / Vapour Pressure Type Liquid expansion / vapour pressure Reasons to affect a liquid / vapour expansion type thermostat: Contact points worn out, burnt out or pitted Loss in manufacturers calibration Phial incorrectly located into pocket The unit c
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Potentiometers Intro

Potentiometers (potential dividers) are a variable resistor which, depending on the function it is used for, can be adjusted either by the end user (electronic thermostat knob on front fascia numbered 1-6 providing the set point, which could be between 54 degrees C and 82 degrees C),
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How to test a potentiometer

To Test a Potentiometer (three pin connector) Note: Manufacturers resistance readings will vary and must be checked for correct operation Electrically isolate boiler / system controls Remove potentiometer wires (at the p.c.b end) to prevent stray resistances from the p.c.b itself (Som
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Potentiometers

… This content is for Annual Subscription and Annual Subscription Special members only. Please login to view this content. (or Register here.)Potentiometers was last modified: May 15th, 2014 by Boiler Fault Finder
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Thermistors

Thermistor faults Thermistors work in conjunction with the user potentiometer (boiler setting for temperature), and the Printed Circuit Board (PCB). A small Direct Current (DC) is sent to the thermistor via the potentiometer, the PCB then knows whether to give more, or less gas to ens
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Fans

Reasons a fan will fail to start No 240V supplying (L) & (N) terminals Burnt out motor windings Worn out bearings Air rotor jammed (on fan casing) impeller heavy with foreign matter accumulation Faulty fan speed control resistor (if fitted)  Burnt Out Motor Windings Electrically i
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Pumps

Reasons a pump will fail to start: No 240V supplying (L) & (N) terminals Faulty capacitor Rotor shaft seized or debris preventing impeller rotation Burnt out motor windings Worn out bearings  240 V LIVE TEST Always check across red or brown and black or blue with multimeter set on
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Boiler System Component Testing for Heating Engineers

System Component Testing

Boiler System Component Testing - for Heating Engineers
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