System Component Testing

Boiler System Component Testing – for Heating Engineers

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...

Cylinder thermostats

Reasons a cylinder thermostat will fail to start

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...

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...

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...

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...

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...

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 to...

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...

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...

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...

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):...

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...

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...

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.

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 h...

Thermostats

Boiler Fault Finding - Thermostats - See also: Cylinder Thermostats Room Thermostats Thermostats Overheat Cut out Thermostats Liquid Expansion Electrical Safety Checks - Resistance to Earth Top Tips for the Heating Engineer...

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 p...

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...

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...

How to test a potentiometer

How to test boiler potentiometers faults and issues for heating engineers and plumbers

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...

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) ...

Pumps

Heating Engineers Fault Finder - Component testing pumps