DIY Doctor UK DIY Forums

I note that you say in your damp and damp proofing section "Outside flues can sometimes cause condensation on the external wall they rise on, check the masonry in this area. (Make sure the boiler is off for this check)."

I had my boiler serviced last year but have recently noticed a white line running down the wall from the flue where condensastion must be forming and there is a damp stain on the bottom brick which is now starting to dry out as the weather is warmer.

I can't tell if it has affected the internal wall as it is behind a sealed kitchen unit.

As far as I can see none of my immediate neighbours have the same problem so what can I do about it?

Depends on the type of boiler you have, if its a condensing boiler the flue may run down, when it should run up so that condensate runs back into the boiler. If thats the case the flue can be adjusted so that it has the correct fall.

If just a combi boiler not alot can be done, does the flue terminate flush with the wall ? would making the flue abit longer solve the problem ?, inside the house should be ok as the flue will be fully sealed.

Thank you for your help- it is not a combi boiler and the flue appears flush to the wall although not very well finished off- to be honest I think my house was put up 10 years ago by some very fed up builders on a Friday afternoon!! The stain starts right under the flue so it could be that some steam is escaping from the bottom of the flue but now the weather is warmer I can't go out and check as steam not being produced at the moment. Glad it won't affect the house internally- was just a bit worried by the dampness on the brick at the bottom.