Boiler flue & rain ingress

Hello,
I think that when it rains hard in a certain direction the flue on my condenser boiler lets in rain water. This then runs through the boiler and drips out from the bottom front corner. Does this sound possible? It is definitely rain water as it never happens when it is not raining.
Any ideas on how I can prevent this?
Thanks,
Graham
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When you consider that the boiler itself should be completely sealed, then the water dripping from the corner of the casing is most likely coming through a gap between the flue pipe and the brickwork of the wall. Is there a collar around the outside of the flue? If not, then some sealant, in the form of some sand and cement mortar, might be a good idea.
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If this is happening you have a serious problem which should be investigated immediately. The flue is connected (obviously) to the combustion chamber and that combination should be totally sealed to the room. It could be water is leaking round the outside of the flue and finding its way into the room from there. But that too should be sealed. Or, of course, the condensate drain if it's a condensing boiler.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

Yes I've experienced similar myself, where I've had a leak at the bottom of the boiler which I've traced back to condensate running back along the (near-horizontal) flue and emerging from the outer sheath of the flue, above the boiler due to a failed 0-ring there. No big safety issue there. I imagine that incoming rain would/could follow the same route.
Also, I've been whinged at by CORGISs about my boiler flue not being far enough away from a facing wall (it's about 0.6 m away) - I've been told that this is close enough for steam/condensate to be pushed back down the flue. If that's plausible, then I'm sure incoming rain is too!
David
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Thanks for all your replies. Luckily the boiler is in the garage and not in the house, but I will put a CO detector in there. The outside of the flue does have a collar and is also sealed with brown silicon. No rain today and no leaks, so definitely rain water.
The water is coming from the front right corner of what the installation manual calls the air box, where the fan and condensate trap are located. Does this provide any clues?
Also on a side note, why do boilers and fires require flues but not gas ovens? I have always wondered about this.
Thanks,
Graham

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They are regarded as small intermittent use devices and they rely on adequate ventilation. There is nothing dangerous given off when you burn gas properly with plenty of fresh air.
It does give off a huge amount of water vapour which will make everything mould if you use it for heating without throwing most of the heat away with ventilation.
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in
and
Boilers are usually sealed units. Where the air is drawn in from outside and expelled back outside through the flue. Not all boilers are like that, but most today are. This reduces the need to have permanently open vents in the same room as the boiler, so keep draughts out when you want it warm inside.
Gas fires and stoves need a permanently open vent from outside, into the room where they are installed. If you haven't go one on an outside facing wall, then provision has to be made for a forced air intake and outlet system into the room where the gas appliance is installed. A gas fire must also have a flue to the outside, with other safety regulations that go along with it.
Did you think it was as simple as fitting a stove in a cupboard under the stairs, and that's it? There is a lot more to gas safety regulations than that. :-)
I'm sure more knowledgeable others will go into more details for you. Telling of how the extraction does this, while the Bunsen effect makes it do that. But I'll leave it there. :-)
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I was wrong, it is leaking from the boiler but intermittently. Maybe condensate then?

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Is the condensate not removed with pipework to the outside? If not, then get a pipe installed to remove it safely to a drain point.
If you have pipework for this purpose, then make sure rain is not overflowing into it and back into the boiler. That may be why you are noticing this problem more when it rains.
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Could be condensate or water from the heating system.
Condensate is relatively corrosive, so steel metalwork it comes in contact with rusts quickly. In time, it can corrode through sealed casings, rendering them unservicable.
With my Keston, I check for leaking condensate by leaving the hosepipe trickling slowly into the end of the flue outlet. The water should pass through and away down the condensate drain. Make sure it is (don't let it fill up the heat exchanger or it will likely damage the ignitor and gas parts). Make sure you don't run water into the boiler air intake instead of the flue outlet.
I don't know how suitable this test is with other condensing boilers. Boilers which pump out the condensate might not do so when the burner isn't firing or the power is off for servicing. At your own risk, as they say.
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Andrew Gabriel
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Thanks for the reply, it begs the question, which part of the flue is the outlet and which is the air intake?
writes:

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Inner pipe out. Outer pipe in.
A bit like "righty tighty, lefty loosey" to remember the way a screw, nut or bolt turns.
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I asked recently about rain ingress as my new boiler has been fitted with a flue that points upwards, about 5 degress from horizontal, which to my mind is bound to see some rain come in.
It was pointed out (helpfully by most!) that that is the right way to fit the flue for the boiler that I have (of course, others may be different). And the same point about condensate was made.
Hope that helps!
Matt
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Today I tried to find the source of the leak, I stripped the boiler down as far as I dared. It seems to be coming down the righthand side of the inside of the air box, between the air box and the combustion box.
So I reckon it is either from the flow or return into the heat exchanger or something to do with condensate from the flue at the top. The condensate trap seems to be filling and emptying correctly and is clear of debris.
The next stage I reckon would be to remove the heat exchanger assembly, but for this I would need to drain down. The wife wants to call someone in, I am near to agreeing with her.
One question, as the water in the system is under pressure then wouldn't the leak drip all the time rather than just when the boiler is operating? If so then it must be condensate, mustn't it?
Graham
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<<<snipped>>>

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Or rain running along the inside of the outer pipe on the flue. Is there any water mark along the inside bottom of the pipe? Or any water marking at all along the flue pipes? If it's condensate, you should see where it has been dripping or running along the metal, as it leaves a bit of a mess behind because of what contains.
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replying to BigWallop, Phillip Ellis wrote: We have had water coming down inside of flue that damages gas valve, replaced twice. Now waiting for the next occurrence! Is there a flue that would prevent it happening?
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On 13/11/2018 12:44, Phillip Ellis wrote:

Golly. Only 10 years old post.
What ever happened to Big Wallop?
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greatest complexity, can seldom accept even the simplest and most
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Yes that website with its total ignorance of the year really is a laughing stock. Brian
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This newsgroup posting comes to you directly from...
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On 13/11/2018 12:44, Phillip Ellis wrote:

Start a new thread, and post details of your boiler make and flue type...
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Cheers,

John.
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