Clunk when switching on hot water heating system - non vented system

[Spirit]

Hi, about 5 years ago I had a new boiler fitted. The location of the boiler was moved so new pipes fitted. No problems. About 2 years ago I then needed to have my 3 way valve replaced, this is when issues began. Initially there was no heat and the system was drained several times, this rectified the heat problem but every time the timer switches my hot water heating on there is a very loud clunking noise, which tells me at 4:30am in no uncertain terms that it has come on! It is literally only one bang but it is extremely loud (wakes me up every day) and not sure if it is me but seems to be getting worse! I have had mentioned to me recently that there is no finger valve to help solve the problem but not really sure what that is. Could anyone give me some advice please as I’ve had 2 different plumbers who don’t seem keen on helping me to solve the problem? Any help would be hugely appreciated.

 

[SJB060685]

Perhaps post a video of this happening so people can get a better idea. Is it only happening on the HW?

 

[Spirit]

Perhaps post a video of this happening so people can get a better idea. Is it only happening on the HW?

Yes,
Only the hot water and only when it is switched on initially from being cold. Getting a video might be an idea but not sure you’d see a lot but hear, certainly hear though!

 

[moonlight]

Is the valve a mid position and the correct way round?

 

[SJB060685]

Yes,
Only the hot water and only when it is switched on initially from being cold. Getting a video might be an idea but not sure you’d see a lot but hear, certainly hear though!

Is this sound localised to the boiler or elsewhere in the system?

 

[Spirit]

Is the valve a mid position and the correct way round?

Yes all the correct way around...

 

[Chuck]

Only the hot water and only when it is switched on initially from being cold.

Could it be expansion noise, i.e. a pipe heating up and 'stick-slipping' against something in the process?