Britony Combi80- Noise when HW turned off (DHW flow switch?)

[russ90]

Have done a search of this excellent forum and the general consensus for similar boilers is that it could be the DHW flow switch.
Could somebody please explain why this flow switch would cause the noise?
Have had problems in the past with sludge build up (all gone now) could this be linked? CH system is clear/inhibited.
Thanks.

 

[kevplumb]

Could somebody please explain why this flow switch would cause the noise?

if it sticks on or turns off slowly the burner wont shut off as fast as it should and the boiler will start to

 

[russ90]

Many thanks for quick response.
I'll suggest that to the technician. Gotta be cheaper than a new heat exchanger!