Worcester Bosch 35CDi II banging & wild pressure (CH onl

16 Feb 2010
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United Kingdom
Hi, just recently our Worcester Bosch 35CDI II boiler has been making worrying noises

After 30 seconds or so of the Central Heating coming on banging/groaning/chugging/train-like noises start and the normally steady grey pressure needle starts waving/fluctuating wildly just below the static red needle (1.5bars).

This only happens with the CH, NOT with HW. :confused:

I've googled but although there are posts about general pressure issues with this boiler there is nothing isolated to CH.

Every 2-3 months I bleed any air from the radiators and top up the boiler pressure but haven't done that for a while - I'll do that tomorrow but as the radiators are usually evenly heated I suspect it's not the problem.

It would be great if it was that simple but if not is it more likely to be a heat exchanger, expansion vessel or some other issue?

Appreciate any thoughts.


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Thats usually the result of a blockage or non operating pump.


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