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Central Heating

Rain water damage to vaillant flue pipe

Our 2 year old ecotec boiler stopped working. F29. Vaillant came to check and found no issue with boiler but apparently there is an issue with the flue (co2 getting back into boiler stopping ignition). Had gas safe heating specialist come to open flue which was full of water. Wrong parts / poor instalation originally meant rain would run into flue pipe.

Question: heating / gas safe engineers tell me the entire flue pipe needs to be replaced (severe water damage to internal rubber? ). The flue is 2 years old. Does this sound about right? I have no clue about heating flues and no reason to doubt the guys but can't help to be supprised if water can destroy the inside of a vaillant flue pipe it in 2 years. Just want to make sure I am jot being taken advantage off in an emergency. Views welcome.

4 Answers from MyBuilder Heating Engineers

Best Answer

Hi if water is returning into the outer part of the flue which is made of steel it will damage the flue and corrode it. Yes it needs replacing as it could be deemed at risk and boiler switched off.


Answered 30th Oct 2020

Sorry I cannot comment on another installers work
I did not inspect the installation so it’s unfair that I should give you a solution
Added to that Gasafe have given their view so I cannot add to their instruction
As an aside I don’t think it’s correct that My Builder is asking installers to pass comment on such serious issues as this


Answered 30th Oct 2020

Rainwater is not particularly corrosive. What is far more likely to be the case is that when the flue was first installed, the flue sections were not pushed fully home into the o-rings or the o-rings were dislodged, ripped or some other issue to do with the plastic inner flue (which holds the corrosive condensate water). Plastic can handle the acidity, metal can't. If the exhaust fumes exiting the boiler through the inner flue mix with the fresh air coming in the metal outer flue then it can be dangerous and can put the CO reading off the scale and/or cut the boiler out. Also, over time the corrosive condensate water dripping from the inner flue leak will rot the outer flue through and then fumes can enter the property which is dangerous. I can't comment on the actual situation as I haven't seen it but it does sound legit that the flue needs to be replaced with all genuine Vaillant flue pipe and fittings and fitted to Vaillant's manufacturer's instructions. I would also recommend that any o-rings are greased when the installer pushes the new flue together. Also, every flue section or change in direction needs to be supported by a proper flue bracket. Badly supported flues coming apart can also cause the issue you are having. Hope this was of some use. Thanks.


Answered 1st Nov 2020

From the information supplied without seeing the job i would agree with the engineer. I have had to change a few vaillant flus due to flu seals failinf after a couple of years


Answered 19th Nov 2020

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