Flue Diff switch - why is it collecting water?

[SeaDoug]

I have a vokera boiler with a flue installed where it's path takes it vertically through the ceiling in to the loft, a 90 degree bend to run horizontally about 1 meter then another 90 degree bend taking it vertical again through the roof. The external flue has a cone 'roof' over a mesh cowal. About half a meter under this is an inverted cone which itself is about 20cm above the roof line.

My problem is that one of the silicon tubes on the flue differential switch is gathering water. Once sufficient water has gathered I guess it interferes with pressure readings and the boiler shuts down (code 08 usually, sometimes 03 or 01). I drain the tube and the boiler fires up quite the thing.

Is there a problem with the flue installation, or is this just a really annoying 'feature' of the boiler? The boiler itself is in a utility room with an extractor fan (not usually on) but also often with drying washing - though I have tried leaving the utility room door open but still I get water collection.

Any one got any ideas before I call out an expensive plumber?

[Mudman]

Just a thought but... Is it condenser boiler?
If so this is meant to happen but the gathered water is supposed to flow out of a drain. Is there a drain on the collector and if so, is it blocked?

[SeaDoug]

It doesn't appear to be a condensor no.. It's a Vokera 730 which can be fitted with a condensor drain if fitting a twin flue (at least that what I get from the documentation I can find!). There's no such fitting on mine and I can't see anything that is obviously a condensate collector or drain..

Thanks for the suggestion though Mudman - had my hopes up for a while - until I got home anyway!

[gucciman]

is this only been happening with the cold weather we have been having lately?

[SeaDoug]

Hi Gucciman..

It's definately got worse with the cold weather - did this a couple of times last year through the whole of the winter. With the current cold spell, it's been going off around 2 or 3 times a day.

What with Mudman's comment and from what I've seen in the tech manual for the boiler, I can't help but feel I need to fit some kind of condensate trap to the flue.. If only to stop me having to get up at 0500 to drain the tube and reset the boiler!

[gucciman]

i'm guessing that with quite a long flue run and with a vertical section the flue gases are cooling and condensing slightly in the cold weather before they can exit the flue.
i've never come across a condensate drain fitted to a flue, but thats not to say they don't exist, you could try and ring vokeras technical helpline and ask them for advice but if your not gas safe registered they may not speak to you, try emailing them if they won't.

[SeaDoug]

Thanks again Gucci, the 'in-line' drain is shown in the tech manual I download for the boiler - but it's apparently only required for a twin-flue system.

I did actually e-mail Vokera tech help a couple of weeks back but heard nothing back.. I'll try again!

As I say, thanks for your input much appreciated.