boiler noise - likely nature of problem

[bilco]

Vaillant VCW242E has recently started making a humming noise when running, sometimes it does, sometimes it doesn't. Suspected either circulating pump or divertor valve but very difficult to localize even by using a rod or similar against them to help conduct sound to ear. Is performing fine in all other respects. Did consider might be a problem with expansion vessel causing excess pressure when hot and this has proven faulty but reducing operating pressure should remove the noise if this was problem and it doesn't.
Have to decide whether I should replace boiler (very expensive option) or simply have a full service (still expensive and could be a waste of money). Can anyone suggest what might be causing this so that can make sensible decission.

 

[JPC]

A service is a service

A fault find is a differnt thing.

A bit like cars.

 

[LUNAT]

HI

could be worn fan.

 

[Boilerman2]

Could also be a noisy coil on the Gas Control Get a RGI in to diagnose properly

 

[bilco]

Hi,

Thanks for suggestions all of which could be helpful but don't seem to quite fit what is happening. To improve my original info - the noise is rather like a loud bluebottle fly and is a continuous tone ( when it does occur which is not always). However, it only occurs when the CH is running, not when the DHW is running so this seems to rule out fan and gas coil. Even when happening it stops if I turn on a hot water tap causing it to switch over from CH to DHW. I'm inclining towards idea that it must be due to divertor valve sticking slightly in CH mode.

Bilco

 

[Agile]

You evidently prefer your own ideas as to the cause!

So I am not very sure that I should even be bothering to reply but as we repair boilers everyday its likely that we will have more useful suggestions as to the possible cause.

We think its something to do with the gas combustion! I come to that conclusion because I know that the boiler works at a higher power on hot water delivery and I think thats is the salient clue.

I dont know exactly what it is on your boiler but on others a similar noise is produced by the modulating coil when the main smoothing capacitor has lost most of its capacitance.

Tony

 

[bilco]

Hi Tony,
Thanks for your further clarification re working harder in DHW mode does seem a likely explanation of what is happening and has brought up a consideration which I hadn't thought of. Will let you know how things work out but, unfortunately, will be away for about 10 days so can't get around to following up on your suggestion until i return.

Sorry if I gave you an impression that I was ignoring and didn't value your and other's suggestions as this is definitely not the case and I am very grateful for all help and suggestions, but, without taking into consideration the additional information you have now advised the symptoms did seem to rule out those causes. Many thanks for persevering.

bilco