System Component Testing

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...

Reasons a cylinder thermostat will fail to start

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...

Boiler Diverter valves issues and faults for heating engineers and plumbers

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) 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) 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...

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...

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 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 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 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 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...

Flow Switch and Its Operation in a Combi Boiler Introduction The flow switch is an important component of a combi boiler that detects the flow of water and controls the operation of the boiler in hot water mode Understanding the operation...

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 (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...

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...

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 / 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...

Introduction 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...

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

What is a thermistor used for in a combi boiler

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) ...

A failure of the circulating pump can cause a number of problems, such as reduced heating and hot water performance, and can result in the boiler shutting down.