The circulating pump is an important component in a combi boiler as it is responsible for circulating water throughout the system.
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.
Symptoms of a Failed Circulating Pump
Some of the symptoms of a failed circulating pump include:
- No heating or hot water – if the circulating pump fails, it will not be able to circulate water effectively, resulting in no heating or hot water.
- Reduced heating performance – if the circulating pump is not working properly, it can result in reduced heating performance.
- Noisy operation – if the circulating pump is failing, it may make unusual noises, such as humming or buzzing.
- Reduced hot water pressure – if the circulating pump is not functioning properly, it can result in reduced hot water pressure.
Steps for Testing and Fixing a Failed Circulating Pump
- Check the boiler manual – Before beginning any work, it is important to consult the manufacturer’s manual for guidance on how to safely diagnose and repair the problem.
- Test the circulating pump – The circulating pump can be tested by turning off the power to the boiler and checking if the pump is rotating. If the pump is not rotating, it may indicate a failure.
- Check the electrical connections – If the circulating pump is not working, it is important to check the electrical connections to ensure they are secure and functioning correctly.
- Replace the circulating pump – If the circulating pump is found to be faulty, it will need to be replaced. This is best done by a professional to ensure the work is carried out safely and correctly.
- Conduct a boiler pressure test – Once the circulating pump has been replaced, it is important to conduct a pressure test to ensure the system is functioning correctly.
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 correct voltage scale.
(If no voltage is evident at pump terminals, check for demand via programmer/timer, room thermostat or cylinder thermostat).
Burnt out motor windings
- Electrically isolate boiler / system controls
- Remove E N L wires from pump terminals
- Set multimeter on Ω scale for resistance readings, across L N at pump terminals:
- less than 100 Ω = replace
- No resistance/infinity = replace
- Approx. 120 Ω – 250 Ω = ok
Note:
A good indication when 3 amp fuses and or “quick – blow” glass type fuses repeatedly fail is when the motor windings have burnt out.
When 240V is present at the pump terminals and the rotor shaft is free moving (anti-clockwise), but still refusing to mechanically spin, then you know the motor windings have burnt out. (This is due to the rotor shaft seizing at some point and causing the pump motor windings to overheat).
Rotor shaft seized
- Electrically isolate boiler
- Remove vent plug on pump head
- Manually, turn rotor shaft (ant-clockwise) several times (Resistance being felt and or not spinning or spinning but with resistance donates a new pump head).
Worn out bearings
- Electrically isolate boiler / system controls
- Remove vent plug from pump head:
- If water severely escapes, bearings are worn out (new pump needed)
- If a small amount escapes, this is to be expected and is quite normal.