Condensing boiler flue dripping internally

[d-dawg]

Hi all,

I've been a keen reader of this forum for a while as we went through various renovation projects. Now finally motivated myself to register and post despite not being an expert (nor a native English speaker), so apologies in advance if any of the description is not clear.

We've been encountering a problem with our boiler flue over the last 1.5 years and several plumbers haven't been able to fix it.

The situation is as follows: we had a new condensing boiler (Vaillant Ecotec Plus 630) installed c. 1.5 years ago, shortly after we bought the property and moved in (this was not planned and - needless to say - an unpleasant surprize). During the installation, it appeared that the old boiler was venting horizontally onto the neighbouring property (contrary to building regs), and the along the new boiler, a new flue was installed venting vertically through the roof of the side extension, carefully making sure it is 600m away from any window. The new flue goes up through the roof, but on the way there are a few joints given the restricted space in the utility room.

Since then, we had occasional dripping from the boiler flue - we essentially see some droplets on the Megaflo cylinder pretty much on a daily basis. It's always at the same spot and not correlated to weather/rain, but rather boiler activity. But hard to see a pattern, and it doesn't always occur when the boiler is running. I think in cold weather it's more often, but also that is not consistent.

Plumbers (Gas Safe accredited) have checked the flue integrity and told us there's no issue and they checked all joints, saying all was fine. One plumber mentioned that it may be condensation from outside the flue (hard to imagine to me).

Admittedly, the leakage is really minor (a few drops every day?), but I wonder if I should live with it and see how it goes, or rather give it another try with yet another plumber? Am i overthinking this?

Any experience/advice/views would be much appreciated - thanks a lot in advance!

 

[DP]

Did your engineer check the air side of the flue
Also the roof flashing, is it proper vaillant product or generic roof flashing.
Is the terminal dedicated item? Should not be white

 

[Madrab]

Where is the Megaflop in relation to the flue/boiler? Can you post a pic?

 

[d-dawg]

The megaflo sits under the boiler, and it’s just dripping on the cap of it, presumably from the flue above. See some pics here, and thanks for the replies.

To confirm: the air side was checked and the flue system seems to be Vaillant, but I don’t know about the flashing.

I should add that we had the roof over the side extension re-slated and new Veluxes installed, but the problem occurred before and after, so don’t think these works caused the issue. They also put insulation around the flue at that time, so that makes access more difficult unfortunately.

 

[Madrab]

The reason for asking is the boiler's internal spaces should be sealed so no liquid should really be dripping from it at all.

So it's just dripping on to the curved top of the cylinder? If so I'd be placing sheets of blue roll onto the top of it and watching it regularly to see where it's actually dripping from, that would provide a starting point as to where to look first, as water always drips vertically downwards.

 

[d-dawg]

Thanks, that I’ve been doing. My suspicion is it runs along the flue and then drips from the joint. There’s no dripping from the boiler itself to be clear, it’s right above the flue joint.

Maybe I just need to watch it, it’s annoying we can’t fix it but I am also getting tired of engineers attending, not finding an issue and then the problem continues…

Thanks!

 

[polesapart]

1 No white should be showing outside. Vertical flue needs shortening. RGI job.

2 Generic flashing used.

Would have been better to have used the Vaillant pitched roof "pantile" flashing - the bottom of the black section of the flue overlaps an upward lip on the pantile to make a weatherproof seal.

3 Clearances of the terminal of the shortened flue to the Velux openings and masonry wall would need to be checked.

 

[gas112]

1 No white should be showing outside. Vertical flue needs shortening. RGI job.

2 Generic flashing used.

Would have been better to have used the Vaillant pitched roof "pantile" flashing - the bottom of the black section of the flue overlaps an upward lip on the pantile to make a weatherproof seal.

View attachment 332587



3 Clearances of the terminal of the shortened flue to the Velux openings and masonry wall would need to be checked.

all depends whether vailllant now allow white showing some manufacturers do

 

[polesapart]

Yes, but I think the issue here is the way the terminal is designed to slot over the flashing.

The adjacent vent with the same flashing is 110mm soil, OD white is 100mm, perhaps a slightly loose fit?
And no "collar" to shed water off the joint.

All assuming, of course, that the OP confirms that this is where the water is tracking in.

 

[d-dawg]

Thanks everyone for the input! I cannot confirm that the water is tracking in from the roof, and I don't think it is. The dripping is coming from an area of flue way before it exits through the roof. Also the water ingress is not related to rain/weather, other than it seems to be more common on cold days. My suspicion is more that one of the joints of the flue is not 100% sealed, but given multiple engineers having attended confirmed flue integrity, I am running out of ideas here.

The boiler and flue was installed by a quite large (and expensive!) company (I let you guess) and has been serviced recently, and all was fine. The length of the flue was indeed decided in order to comply with the 600mm distance to the windows, party wall and our own masonry wall.

Probably there's no way around finding yet-another Gas Safe accredited firm to have a look at it then...

Happy Sunday!

 

[gas112]

Yes, but I think the issue here is the way the terminal is designed to slot over the flashing.

The adjacent vent with the same flashing is 110mm soil, OD white is 100mm, perhaps a slightly loose fit?
And no "collar" to shed water off the joint.

All assuming, of course, that the OP confirms that this is where the water is tracking in.

those lead slates with rubber collars are not the best but providing the hole has been cut properly they will provide a perfect seal .
The OP has said drip is there regardless of weather so personally i would be taking the flue apart and looking for a faulty inner flue seal which doesnt always show up when using just a FGA to check the flue .
That would be after making sure drip is coming from flue and not the boiler

 

[DP]

Yes, but I think the issue here is the way the terminal is designed to slot over the flashing.

The adjacent vent with the same flashing is 110mm soil, OD white is 100mm, perhaps a slightly loose fit?
And no "collar" to shed water off the joint.

All assuming, of course, that the OP confirms that this is where the water is tracking in.

Happened to me where water ingress was through the rubber

Looks like the terminal has been butchered