DIY Doctor

Damp wall due to combi boiler exhaust

Postby ergolargo » Wed Mar 16, 2011 1:58 pm

Hello all

Can anybody advise about the best course of action? I have a combi boiler that has its flue exhaust going out through the wall, but it appears that over time, the steam from the flue has had a damping effect on the external wall over a stretch of a good few metres above the exhaust. The paint has started to flake away, but most importantly, it looks like some of the moisture collects under an exterior windowsill about 3-4m above the exhaust, and this has eventually become a problem at this location, in that the damp has crept through to the interior wall, giving us a damp patch under the window on the inside. Although it is only a small damp patch at the moment, I am thinking it would be best to try and get a new flue exhaust, or better still just a new terminal guard, that might include a solid upper surface that would act as some sort of directional 'hood', to push the steam exhaust further away from the wall before it can rise upwards.

I have a feeling this would go a long way to sorting out the problem - I don't think it is rising damp in the normal sense, the wall beneath the boiler seems to be fine, and there seems to already be an additional damp proofing membrane in the wall above the exhaust at a height of about 2m, which doesn't seem to be preventing the problem, which would be consistent with the theory that it is moisture settling on the wall from the steam. Maybe this is just another sort of membrane though, I don't know enough about damp proof coursing to know exactly what it is.

Does anybody know where I could get a new terminal guard with some sort of directional hood that would help with this problem, and also, if there is any useful anti damp product that can be applied from outside to try and reduce the existing damage?

Thanks very much for any suggestions.


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Simply Build It

Postby szaadchim » Fri Jul 08, 2011 11:53 pm

we had our boiler vokera 80 shut down couple of months ago,

just noticed month ago the wall joining the kitchen wall in lounge got damp and slowly increased and all black now , got surveyer coming to check

suddenly i thought even though my boiler is off it can be my boiler then i saw at the flue which is going outside has a damp and removed the wall paper and then can see that all black and damp there
started thinking that our boiler is off and heating is off but when we use the hot water tap, even though there is no hot water in that its just easier we found as its on left hand as we knew it doesnot matter as the water is cold on both tap, but there is hissing noise from boiler that water is coming from there or so , never thought about it but after reading some articles about combi and condensing etc , realised or think becasue its condesing boiler its got something to do with water and vapor or something like that , as boiler is off but i am still using hat water tap and its going through the boiler so its doing somethig to the boiler and which in truns sending water or vapor or condese in the flue or wall
any help would be much appreciated
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