Combi flue dripping despite fall back to boiler

[gooseborry]

Hello, my new Vaillant combi boiler flue is dribbling water when it is on.

Most notably when it first fires up, the stream of gas pushes about a tablespoon of condensate out. Then it intermittently drips after that, leaving a noticeable wet patch on the floor.

Now the confusing thing is, the flue is definitely slopping back to the boiler, I can verify this by looking inside and seeing the condensate draining away.

But it seems a lot of it is just beaded to the edge of the flue, and is just waiting there to be pushed out when it fires up.

Installer adjusted flue today giving it more drop, but it's still dripping.

Would the cold snap be causing this and it should go once temps rise again? Or is something not right here?

Thanks

 

[cross thread]

Common problem especially with the colder weather

 

[MJN]

Even despite the back slope there's still surface tension of the condensate as well as joins/seams etc that will prevent absolutely everything from draining back down the flue.

 

[jordanm23]

Hello, my new Vaillant combi boiler flue is dribbling water when it is on.

Most notably when it first fires up, the stream of gas pushes about a tablespoon of condensate out. Then it intermittently drips after that, leaving a noticeable wet patch on the floor.

Now the confusing thing is, the flue is definitely slopping back to the boiler, I can verify this by looking inside and seeing the condensate draining away.

But it seems a lot of it is just beaded to the edge of the flue, and is just waiting there to be pushed out when it fires up.

Installer adjusted flue today giving it more drop, but it's still dripping.

Would the cold snap be causing this and it should go once temps rise again? Or is something not right here?

Thanks

Did you ever get this resolved?

I have the exact same issue. The boiler was installed a year ago - just got it serviced and it turns out the flue was not cemented in and the run was not correct. Had another company out to do the service as original fitter has disappeared off the face of the earth.

They corrected the run but it still pushes out about 5-10 drips when firing up. It almost looks like it is gathering a small amount of water in the end of the terminal which is then being pushed out when it starts up.

 

[kidgreen61]

Why does this bother you?
It's only a few drops of water.

 

[jordanm23]

Why does this bother you?
It's only a few drops of water.

It's falling onto a natural stone patio and i've heard gas engineers say they've seen it eat into brickwork and patios.

The odd drop would be fine but 5-10 drips dribbling/spluttering every time the boiler is fired is soon going to add up.

 

[Lower]

Condensate is acidic and will burn a hole in stone or concrete.

you may be able to get an upswept bend that goes on the end of the flue.

 

[dilalio]

It's falling onto a natural stone patio and i've heard gas engineers say they've seen it eat into brickwork and patios.

The odd drop would be fine but 5-10 drips dribbling/spluttering every time the boiler is fired is soon going to add up.

Put a planter there.
It happens a lot.
All things that emit warm humid air into a cold environment will produce a dew point and the amount of condensate produced is not just from the combustion process but also from contact with hot gas meeting cold air.

Likely to overcome the backfall and design of the terminal nose.

I'd expect it to be diluted not pure condensate if you get my drift?

 

[jordanm23]

It seems like a crazy amount though.

To me it seems like it's not the condensate generated when the boiler fires, it's already there in flue terminal and then gets jettisoned out when it fires up. Flue is definitely sloping back towards boiler slightly but the terminal bit looks a bit more straight on - is that bit adjustable (obviously not by me... still trying to get ahold of the engineer who did it ).

 

[ianmcd]

/spluttering every time the boiler is fired is soon going to add up.

Then you have a condensate discharge problem nothing to do with the flue, if the boiler is spluttering, are you sure that the noise you are hearing as the boiler starts is not just the pump trying to move trapped air in the system water ?

 

[jordanm23]

Then you have a condensate discharge problem nothing to do with the flue, if the boiler is spluttering, are you sure that the noise you are hearing as the boiler starts is not just the pump trying to move trapped air in the system water ?

Sorry - might have worded that weird - I haven't heard a spluttering noise... it is spluttering water out of the flue terminal (boiler is in the loft but I haven't heard much noise from it when firing up).

Sometimes the water dribbles out of the end and other times it spits/splutters out.

 

[dilalio]

To me it seems like it's not the condensate generated when the boiler fires

Yes! This is what I was getting at in my post. It's more "dew" that is being produced at the terminal.

the amount of condensate produced is not just from the combustion process

 

[jordanm23]

Yes! This is what I was getting at in my post. It's more "dew" that is being produced at the terminal.

Should it run back to the boiler though or drip out? Any ideas on if the terminal of the Valliant flues are adjustable so it can be lifted ever so slightly?

 

[Madrab]

You can always get a little condensation that's sitting near the end of the flue or a little rain that's been caught being forced out by the fan pressure when the boiler starts up, I have an upswept flue diverter on my flue and even it does it sometimes.

Most of the condensate from the flue will run back down into the HEX but there can always be some moisture near the end of the flue that is blown out. As suggested you may find that it's is less concentrated than the condensate that is drawn out of the gasses and runs out through the condensate pipework. Another point to note is ensuring the system is set up properly to ensure that most of the condensing happens in the HEX and not out in the flue

If you are really worried then test it with some litmus paper and see how far off of neutral it is and whether it's worth bothering about.

 

[jordanm23]

You can always get a little condensation that's sitting near the end of the flue or a little rain that's been caught being forced out by the fan pressure when the boiler starts up, I have an upswept flue diverter on my flue and even it does it sometimes.

Most of the condensate from the flue will run back down into the HEX but there can always be some moisture near the end of the flue that is blown out. As suggested you may find that it's is less concentrated than the condensate that is drawn out of the gasses and runs out through the condensate pipework. Another point to note is ensuring the system is set up properly to ensure that most of the condensing happens in the HEX and not out in the flue

It's been an ordeal with this flue
Original installer had not cemented the flue - just had the rubber weather shield thing on it. It had been dripping originally and he came out to adjust the flue angle... and in doing so forgot to put the self tapping flue screws in - so essentially the flue was not secured and could just be pulled out.

He had also put the PRV through a plastic tundish and connected to the condensate which feeds into the internal soil stack. Turns out rather than fit tunish into a connector, he had pvc welded a piece of pipe into the connector which was of course the same diameter as the end of the tundish and then rammed it in causing the connector to crack (had the PRV ever blown off it would have just p*ssed out into the loft space).

After he disappeared we got some other local engineers out who said everything else looks fine - just those issues above and they have corrected the flue angle, binned the tundish and diverted the PRV outside with a mushroom cowl.

Got a hold of them to mention the new dripping and they said they'll come back and see what needs doing to stop it