noisy central heating system

[anthg]

I have a BAXI combi boiler which is approx. 3 years old. There has always been an irritating knocking noise coming from the pipes within 10 seconds of the heating being turned on. The noise repeats itself every 5 minutes or so whilst the heating is on and stops as soon as the heating is turned off. It's difficult to pinpoint where the noise is actually coming from but it can be heard in every room in the house.

I've read on this website that it could be due to pipes expanding and contracting but if that was the case would it not take a while for the pipes to heat up and cool down.

Is it possible that there could be air in the system causing this noise?

 

[Meldrew's mate]

I'd say just as you did, pipes expanding & contracting. Just after hot water is drawn will be the noisiest if it is.
Test by turning the boiler temperature (CH) down low. With the flame off and the pump running it will separate the mechanical noise (water moving, air in pipes, resonating pipes) from the expansion noise. Turn the temp up again. Does the noise return when the flame is on?

MM

 

[anthg]

Thanks for the advice MM.

There was no knocking with the temperature turned down so it must be expanding pipes.

I'll have to lift some floorboards and try to find where the problem is.

Many thanks.