Combi Flue causing excessive condesation

[Pipemangler]

I have installed a Biasi HE32 Combi Boiler which vents through the loft space to an external wall. As the flue length is quite long (3m) through a cold space we are finding that condensation from the flue is draining back through the boiler, as there is no condensation trap in the flue.

Is the answer to fit a condensation trap in the flue (biasi do a fitting for a vertical flue, but not a horizontal one) or is something else happening that I'm not aware of?

Regards

Rupert

 

[stem]

Condensing boilers are so efficient that they cool the flue gasses to the point that they condense inside the boiler. This condensation in drained away by a pipe from the boiler.

If the flue on a condensing boiler is horizontal, it slopes very slightly upwards towards the outside. (non condensing boilers slope downwards) This means that for a condensing boiler, any condensation in the flue runs back into the boiler, where it exits via the condensate drain.

I imagine Biasi offer a condensate trap for vertical flues for use with non condensing boilers as they don't have an internal drain. A horizontal flue would run downwards and not need one.

I am concerned when you say "I have installed" because the fact that you are asking the question shows that you don't have sufficient knowledge to install a boiler, so I'm assuming that you mean a suitably qualified Gas Safe registered professional who knows what he's doing has installed it for you, and you are asking out of curiosity.

 

[Agile]

Under normal conditions with a condensing boiler flue condensate would only occur in the inner tube which would be harmlessly disposed of by the boiler.

Where EXACTLY is this condensate going to?

I suspect you have fault in the flue installation and this is most likely if it has not been professionally fitted.

What is the angle of the flue extension pieces and of the final section and does the terminal exit horizontally?

Tony

 

[Pipemangler]

Under normal conditions with a condensing boiler flue condensate would only occur in the inner tube which would be harmlessly disposed of by the boiler.

Where EXACTLY is this condensate going to?

I suspect you have fault in the flue installation and this is most likely if it has not been professionally fitted.

What is the angle of the flue extension pieces and of the final section and does the terminal exit horizontally?

Tony

The flue is angled upwards I haven't measured the angle but it is a shallow slope.

The final section exits horizontally.

The internal condensed gases are collected and disposed of through the internal drain trap and are fine.

The first couple of days after fitting there was an excess of condensation coming from the outer section of the vent and this collected in the boiler and this is how I noticed it, as we had water dripping from the boiler. Not a lot but more than none!

This has now ceased but I am interested in how it may have happened and whether this is a known issue and do I need to get someone to look at it or is it just a passing issue?

Also the boiler was fitted immediately prior to the coldest weather we have had in some years at the beginning of December, so could this be a contributing factor?

Regards

Rupert

 

[Agile]

Nothing you have said indicates that anything is wrong with the slope of the flue.

However, the physics of the situation should preclude any condensation within the outer inlet part of the flue as thats heated during transit so should certainly not be condensing.

Nowhere do you indicate where the gas registered person was involved with the installation! ( or ? )

I am left wondering if one ( or more ) of the flue joints are leaking as this will certainly create condensation.

The test for this is to measure the CO² percentage at the inlet test point at the boiler and see what this reads.

That will normally need a gas registered person with a flue gas analyser which all competent installers should have for use on commissioning and fault finding on boilers.

Tony