noisy worcester 24i boiler

[philly23]

boiler only 4 years old, started to make extremely loud knocking noises when central heating selected, ok with hot water, had a engineer replace water pump but 5 mins later same noise. had a new radiator fitted , small cloakroom suite and piping for washing machine but this was 2 months ago and all was fine. also pressure needle flickers like mad when noise omitted any help would be very much appreciated

 

[ChrisR]

Then look for something else which restricts flow on CH but not on HW. Filter in the CH return?

 

[philly23]

thanks for the reply, are there any simple checks i can perform, apart from bleeding radiators which i have also done, also turned off new radiator just to eliminate this

 

[Agile]

You can check to see if there is a blocked filter in the CH return as chris suggests above!

Tony