Concentric Flue and rain

[megawatt]

In a similar vein to post

//www.diynot.com/forums/viewtopic.php?p=585134#585134

Which was well answered thank you ...

What stops rain running down the inlet into the boiler as the fan only expels gases out the outlet and the flue slopes downwards 3 degrees towards the boiler?

I shouldn't concern myself about such things I know but I'm curious ... I must have some obsessive curiosity disorder

 

[Gasguru]

Nothing on most boilers.

Some have a flue outer duct design that helps a little in stopping water ingress ie openings underneath or an extended cowl.

I did see a Baxi Duotec (at a trade show) with a purpous designed tray to catch any water from the air intake. However whether it made it to final production after their accountants realised it would make the boiler a litlle more reliable....

Personally a little water ingress always helps to generate spares revenue and repairs which is good for the industry yes its is that immoral

Some Worcester Greenstars suffer big time (££££££££) from this problem.

 

[megawatt]

Given all the high tech design that's gone into recent condensing boilers it seems a little odd that they're happy for the thing to drown and flood the kitchen when it rains

My brother-in-law has just had a Greenstar 440 fitted (big floor standing combi) ... Does he need to be worried?

 

[ACOperson]

I've seen a Glow-Worm with a very long flue run with rusty spots at almost every flue joint. Water ingress along the outer flue pipe.

 

[esra_ptrap]

I'd be interested in your experiences with Greenstars and water ingress Gasguru as I haven't come across this problem.

The latest 440 uses the Condensfit fluing system which has a raised profile on the inside of the outer casing about 2" in from the terminal.

This profile is about 5mm and when the flue is angled at 3 degrees down towards the boiler water should gather in the 2" between the terminal and this profile and drain away to the outside through the bottom of the terminal and not pass down into the boiler.

Wouldn't work if you pointed a hosepipe at it though.

 

[Gasguru]

With standard efficiency boilers all flues sloped downwards away from the boiler and unless it was installed incorrectly water could not find its way back to the boiler.

With condensing boilers most flues slope towards the boiler (although with some short flue kits the outer duct is set horizontally and just the inner duct slopes towards the boiler).

Therfore unless the flue terminal is well designed and fairly sheltered water will find its way back to the boiler. The outer flue duct is not normally well sealed at its joints so they can leak and if the water finds its way back to the boiler severe damage can occur.

In regard to Greenstars there were some postings regarding burnt out fans on the Juniors. The flue terminals may now have been modified.

Install a boiler near Dartmoor where the rains horizontal and most designs will be waterlogged.

And don't forget water ingress via the condensate pipework. At least half the condensing boilers I come across have not had the pipework installed correctly increasing the chance of flooding back to the boiler. Customers aren't too happy as its a turn off/warning notice unless they agree to installing it properly.

 

[Rob]

//www.diynot.com/forums/viewtopic.php?p=477492#477492

My experience. Took a new flue (modified) flue to cure. Rain guard helped for a couple of weeks, all new worcesters now have the new flue with black terminal.

 

[esra_ptrap]

I actually live on Dartmoor National Park

 

[ChrisR]

I actually live on Dartmoor National Park

It'll be the dogs of all those bloody hikers peeing in sideways, then.

 

[baxpoti]

I did see a Baxi Duotec (at a trade show) with a purpous designed tray to catch any water from the air intake. However whether it made it to final production after their accountants realised it would make the boiler a litlle more reliable.....

Yes it did make it!

 

[Gasguru]

So how come it did'nt make it onto the Platinum range? - you'd think the extra cost (say 20p) to put it on would be worth it when they are offering a 5 year warranty.

I've worked at Southcott (near Okehampton) - proper horizontal rain there. At least its all oil.

 

[esra_ptrap]

It'll be the dogs of all those b****y hikers peeing in sideways, then.

That explains the smell ... I thought it was the wife's cooking

For the OP: I also currently have a Worcester Greenstar 440 floor standing combi and don't have any problems (even with the horizontal rain )

Key thing for normal rear fluing through a standard double skinned wall (where the flue length from boiler to terminal is about 360mm or so) is to fit the flue horizontal. The inner exhaust outlet will by design then be sufficiently sloped downwards back towards the boiler and condensate capture works well whilst allowing any rainwater which enters the outer casing to be captured by the raised profile I mentioned earlier and drain away outside.

Worcester should IMO make this clearer in their installation instructions as they do give the impression that the entire flue should slope towards the boiler by 3 degrees ... If you do this the potential for water ingress is obviously higher.

 

[Gasguru]

Had a look at an Alpha CD24S condensing system boiler today. There is a catch tray for water ingress under the air duct with a pipe connected that leads straight down to ....... the bottom of the combustion chamber. Just floods a bit further down

Although the outer flue duct collar onto the elbow doesn't properly seal so water probably run out and just rot the top of the boiler instead.