worcester greenstar 30si problem loud clunk noise

[kwr4b]

Hi need some advice!

My boiler fires up when i turn on the hot tap and everything is working well(plenty of hot water). However, when the hot tap is closed the boiler sounds like it still runs for about 10 seconds before a really loud clunk. Sounds like a water valve is closing within the boiler and it is heard right through the house!!
The boiler is 2 years old now and i think this noise has been there since day one. It is only now that its really starting to bother me as we now have a baby to get to sleep.

Thankyou!!

 

[boilerdoktor]

hi pal

this sounds very like the boiler bypass. If it is in warranty call wb out if not you can close the bypass in the boiler but only if you have a bypass rad in the house ( one which is perm open without a TRV)

If you look under the boiler where the pipework is look under the pressure release valve ( back right of boiler a valve with a red plastic lever)

under there you will see a slotted plastic switch?isolation type of thing

take flat headed screwdriver and turn quarter turn and this closes off the bypass.

the clunking is caused by the non return valve at the bypass.

 

[swa110w]

Hi, this is a bit of a longshot three years later but did OP ever solve the problem? Did the advice here work?

We have the same problem but instead of a clunk it was more a series of tapping after demand.

Our plumber, who was initially stumped, tried turning off the bypass in the boiler (as outlined above).

This quietened the noise a bit but it is still there. We are also expecting a baby, so we're quite keen to minimise the noise!

Our plumber reckons the next step (if we can't put up with the noise) would be to try replacing the manifold?

Just wondered what OP had done...