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Central Heating

Combi boiler banging what's the cause?

We have a Baxi Duo Tec 40he combi 4yrs old, it started to lose pressure every day, our usual engineer came out and said the vacuum tank was full of water, removed this and refilled with air, he said to 1bar, heating came on no problem and pressure did not drop. We had noticed previously that the hot water was fluctuating, not by much, hot then luke warm back to hot. After the system was refilled with air, when the hot taps are opened the boiler bangs very loudly, hot water going cold then hot and the bathroom and 1 bedroom radiator gets hot. The engineer was told of the problem and he now says the heat exchange unit needs replacing at a cost of £120, is this feasible, we dont understand why the radiators are getting hot. He has said he wont charge if this does not fix the fault, what we are concerned about is that there will then be another fault, more money, can you advise ?

2 Answers from MyBuilder Heating Engineers

Best Answer

From what you have described it sounds like the the heat exchanger is sludged or scaled up and would need to be replaced. I would say £120 seems very reasonable.
The engineer should be able to show you signs of scale or sludge on the entry and exit point of the plate to plate heating exchanger.
I would suggest if you are in a hard water area and it is scale then you need to look at some type of scale reducer.
If it is sludge related then you will need to look at having the system flushed and inhibitor added.
Otherwise the problem will just come back over time and you will need another new heat exchanger.


Answered 29th Nov 2012

The expansion tank may be a semi sealed unit which has a diaphragm in the centre they sometimes split or have a tiny hole allowing pressured water to pass.


Answered 28th Nov 2012

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