Condensing Boiler Flue Issue

[Walmtech]

Hi I had my Combi Boiler replaced a little over a year ago with an Ariston Micro Genus 32 HE. The previous boiler was the non condensing 27kw version. Now the boiler is working fine probably good for about another 2 weeks being an Ariston 😀 Obviously this flue produces a lot more vapour clouds - highly visable as well. Somehow I am now getting some condensation in my loft space when its cold - a lot at the moment then! This is a concrete tile and felted roof with flush eves. There is also a two vent tile in the roof space but I have blocked them up for a few days to test and it made no difference the condensation is still getting in some how. It is not constant it may be do do with direction of the wind? I think the condensation is getting in at the junction of the roof with the plastic facia board. I am reluctant to try and seal the eves with expanding foam or something as I want to allow the timber to breathe.

Anyway what I was thinking to try and cure this was adding onto the existing standard horizontal flue 60/100 (Cut down to about 80cm long) add a 90 degree bend and a standard vertical flue kit with a support bracket fastened to the facia this should move the discharge high enough hopefully to not get back in the building? I have seen that you can get anti plume kits but not sure if these can move the flumes easily above eve level? Any suggestion greatly appreciated.

 

[oldplumber]

you own a cold roof in insulation terms ie the insulation is btween the joists and therefore anyheat that does get through onto the cold roof itself will cool and produce water as its dewpoint is lowered giving condensation. blocking your airvents will immediately make things worse as there wont be any air flow to remove the now very moist air in the roof space. This exacerbated by the stunningly cold weather weve had recently.

Your only cure is to convert to a warm roof set up, ie fit insulation between the roof joists so that the warm air doesnt hit the cold roof. Some what costly, so your better off increasing your eave vents and pushing more fresh air through the roofspace.
As far as the boiler fumes sneaking back into the roof, not an issue and as regards playing with the flue, just leave well alone or get back your installer for advice, Im sure hell add plume kits for you at your expense, but its not needed.

 

[Walmtech]

You quite right it is a cold loft space I replaced the original ceiling joists with six inches ones and have six inches of rock wall insulation and the roof space is fully boarded out. The ceiling below being a kitchen and a bathroom was all finished with foil backed plasterboard which I even taped the foil joint between the joists of so I am sure water vapour from the house is not the issue here. Also the problem only started when the boiler was replaced no other work was carried out and for 7 years before and with the a non condensing boiler I did not have the issue. I have trapped some of the condensate on a metal plate and it is slightly brown not sure if that proves anything? Also I don't have eve vents as this is a flush eves the only ventilation to the loft space is the ventilation tiles. Unfortunately the original installer has moved overseas so I thought I would see if I could get some advice here before approaching any tradesmen most of whom I know from previous experience are just going to laugh due to the fact its an ariston boiler.

 

[oldplumber]

ais it a breathable felt if not half the problem. roof spaces in general get a lot a condensation esp now its cold and youve a kitchen and bathroom below. check vent tubing not holed one thought. cant believe its the boiler flue as what you see is vapour plumng away and if it was getting into the roof youd se the vapour plume clearly. After all the old boiler gives off flue products one of which is water and that too would have caused problems of condensation previously. Look more at venting the rof more, more likely your new insulation has b;ocked previously leaky eaves etc and created a problem,, Rooves need to breathe if they arnt hot types.

 

[tamz]

Your loft will always be slightly warmer than the outside air and there is always a condensation risk. Think single glazed windows! The only cure for this is more ventilation. Condensation is usually accentuated in the area above your loft hatch as this is where most heat gets through.
It is not boiler related.

Better speak to a builder or roofer.

Btw. Aristons are ok. I've even got one myself (got it as a freeby) It has not missed a beat in 3 years and i have never as much as looked at it.
First time it coughs it is binned tho 😀

 

[Walmtech]

Thanks for the advice will look at other possibilities for the condensation getting in then would much rather it wasn't the boiler as the rest of the issues I can sort myself. I actually think it is adequately ventilated as it is very drafty in the loft space. If it was condensation from the rooms below then would expect it to condense in the 6" of rockwool as that is where the dew point would be. One thing I need to check is the ducting for a shower extractor and for a kitchen hob extractor that run though the ceiling - the reason I haven't checked yet is they are under the loft boards and the problem only started shortly after the boiler was fitted so I just reasoned it was that but guess should check all other possibilities before paying silly money for flue adjustments!

Had an Ariston boiler before like I mentioned it ran fine for 5 years then started playing up. I was short on budget and cold when I had it replaced a year last November and getting it swapped for a newer model of the same boiler was so much cheaper than the better alternatives almost zero plumbing involved just a connection to the sink trap for the condensate trap. If I get 5 years out of this boiler at the price I paid I will be happy enough.