Combi boiler vent on roof freezing up

[Flo]

We had a new condensing "VOKERA COMPACT HE" boiler installed a few years ago .unfortunately the company went bust so we can't ask them.the first winter the roof vent almost froze right up .the icicles hanging from the vent were extensive.the boiler never stopped working so I hoped it would if the vent eventually became frozen shut....is that correct .? Anyway during the last cold spell I decided to keep the boiler on low and on all the time but it didn't matter .the vented fumes still turned to water then froze over.i have no idea why nobody else in the street with a roof vent seems to have this bother and why doesn't the vents on other people's houses that are fitted on side walls have similar problems......

 

[AMGasServices]

Are you referring to the boiler flue or air vent ?

 

[diamondgas]

We had a new condensing "VOKERA COMPACT HE" boiler installed a few years ago .unfortunately the company went bust so we can't ask them.the first winter the roof vent almost froze right up .the icicles hanging from the vent were extensive.the boiler never stopped working so I hoped it would if the vent eventually became frozen shut....is that correct .? Anyway during the last cold spell I decided to keep the boiler on low and on all the time but it didn't matter .the vented fumes still turned to water then froze over.i have no idea why nobody else in the street with a roof vent seems to have this bother and why doesn't the vents on other people's houses that are fitted on side walls have similar problems......

Sounds like you're describing a vertical flue outlet yeh? I've noticed exactly the same on several condensing combi's. Down to the amount of condensate leaving the boiler and condensing as it leaves? Fumes evacuate differently from a vertical flue than from a horizontal. There's a larger surface area for them to condense on and I imagine this is where the water vapour forms in to droplets and gravity does the rest along with below freezing temperatures! The fume temps from conventional boilers are much higher and don't condense till they're away from the terminal.

 

[Flo]

Are you referring to the boiler flue or air vent ?[/
my mistake its the boiler flue on the roof that iam referring to.it looks like a black plastic tube about a foot long with rain cover.

 

[Flo]

Thankyou ,,,,,but I still am unsure if there is anything that I can do to prevent this from freezing up as in heating on all the time or intermittent or a different type of flue or re route the flue to outside wall.that would involve a long 3metre run of pipe which I have been advised against because iam told its meant to be the shortest route outside

 

[Flo]

Yep.its a vertical flue outside

 

[diamondgas]

Thankyou ,,,,,but I still am unsure if there is anything that I can do to prevent this from freezing up as in heating on all the time or intermittent or a different type of flue or re route the flue to outside wall.that would involve a long 3metre run of pipe which I have been advised against because iam told its meant to be the shortest route outside

I can't think of anything you could do to prevent this happening. Re-sighting the flue would be my thoughts too!

 

[stevetheplumber]

im unsure what the problem is do you feel its dangerous or unsightly?

 

[AMGasServices]

How far away is your boiler from an external wall ?

 

[Alpha man]

Could you take a pic of the flue outside and post it up on here?

 

[Roger Welton]

Increasing the flow temps (should) increase the flue gas temp above that of the dew point (55 degC), though you will use more gas as it isn't as efficient.

 

[Flo]

How far away is your boiler from an external wall ?

The boiler is about 3m away from an outside wall but is it safe or advisable not to take the shortest route outside .if it was legal or safe I rekon taking the vent pipe up into the attic and then out the eaves via a vent and facing downwards to the ground is an option but is it safe practice

 

[mountainman]

Get a professional in from this forum.
It may cost a few quid but it'll be worth it.

 

[Flo]

I feel it's more dangerous than unsightly .i just don't want it freezing right over the end of the flue and the boiler doesn't cut out then I don't want to think what might happen .maybe paranoid due to lack of knowledge here.in actual fact during the last cold winter two years ago it was covered in icicles and I then had a separate problem.thanks to the air vents in my eaves I noticed I had a water problem.the water was dripping out of my eaves air vents and turning to ice.i went up into the attic and the eaves were Full of water which I rekon was coming down my roof from the flue being backed up so this is another concern of mines but it has never happened again.that day I had to drill into the eaves to drain off the water and eventually those wooden eaves got replaced by PVC eaves.
So I have to wonder how the water backed up and ran down between my tiles and felt on the roof and collected in the eaves .mind you the roof was also covered in deep snow which might have worked its way through the flue cover on the tiles. I don't now if that's more of a likely possibility .

 

[tamz]

It is extremely unlikely it would ever freeze enough to block. The icicles would have been hanging form the bottom rim of the air intake.

If it ever did, your boiler would cut itself off.