Loud Boiler Noise

[nottaclue]

hi i have a combi boiler that up till now has been fine. Just recently it has been making very loud knocking/gurgling (like when a kettle is initially boiling) noise which sounds like its coming from the pipes at the boiler, the bar pressure gage also jumps all over the place. This happens about 2 - 5 mins when the central heating is turned on and i've found i can get rid of the noise if i turn the bathroom hot taps on although the noise returns shortly after i turn them off. I have tried bleeding the rads and am unsure what to try next.

Hot water for baths/showers is fine no probs and the heating does work when the noise occurs but obviously something is not right.

Any ideas welcome.

Thanks

 

[gas4you]

Could be DV sticking in DHW mode.

Make and model would help

 

[nottaclue]

Thanks for your reply sorry for missing that out. its a worcester junior 28i its 3 years old.

could you possibly ellaborate on what DV and DHW mean if thats a possible problem i'm afraid im not very knowledgable.

 

[Gasguru]

The Junior it doesn't have a diverter valve.

Check the pump (in the boiler) is set on speed 3

Are the flow and return valves underneath the boiler fully open?

Otherwise sounds like blocked heating pipework or sludged up pump (the pump is only used for heating).

 

[nottaclue]

Thanks, I'm not sure how to check the speed settings of the pump or even how to get to the pump. I guess the valves are open unless they can close of their own accord? it has been fine up till recently.

I have a engineer from worcester coming out on Thursday to do the 1st inspection for a service contract. It may be I have to pay for anything wrong with the boiler before the service contract starts. Is what's been suggested expensive?

Thanks again

 

[Gasguru]

Pop off plastic shroud around controls.

Remove 2 screws.

Lift off outer casing.

Check pump on right hand side is set to speed 3. look carefully at the switch on the pump.

 

[nottaclue]

thanks gasguru will do and i'll post back tomorrow with answer

cheers for the help

 

[nottaclue]

Took the boiler cover off and confirmed the pump was on setting 3. I also release the valve on the pump in case any air was in there. Put heating on and the noise happened as usual. I put the pump setting to Speed 2 and i now get No noise. My question now is with 8 radiators in the house can i get away with it being on setting 2 or does is have to be on 3? What are the possible implications of this if any.

Thanks in advance.

 

[Gasguru]

Worcester technical could never make up their mind when I asked them about setting the speed lower on this model (the manual says set to 3).

The pump is only used for heating (and a short overrun after DHW drawoff) and running at speed 3 is way to high for small systems.

I think the boiler software (combined with slow thermal response from the sensors) is poorly designed and suggest you run whatever speed keeps the thing quiet.