A plumber once told me that the energy efficiency statistics for condensing boilers would not look so impressive if they included an allowance for the diesel for his van every time he had to go and fix the things. He may have a point in that there is an epidemic of problems at the moment because the pipes draining the condensate to the outside are freezing in the very cold weather and the condensate is backing up into houses, flooding floors and in some cases damaging the boilers. This may be a particular hazard where people are away from home and have left the heating running. My local heating engineer said he had 10 calls about this problem before 9.30 one morning recently. EVeryone I've mentioned it to has looked and found the outlet pipe frozen. I know we don't often experience such low temperatures but is there a simple way of avoiding this problem? I now know several people who (like me) have had to disconnect the pipe and allow the boiler to discharge into a bucket.

I think I'm right in saying this pipe should be insulated outside if under a certain size (32mm) til it reaches the drain
It should also be routed internally as much a pos. keeping the external section as short as possible

Insulating the pipe is clearly a good idea but the water emerges as a trickle and freezes as it meets the outside air, so I don't think that's the answer when the temperatures are as low as they have been recently. Vigilance and applications of hot water will help, but that's not always possible.

Posted By: davidfreeboroughI don't think we should blame the condensing boiler for a poor installation. As far as I know, there's no reason to take condensate drains outside. They can be connected internally to the kitchen/utility/bathroom waste.
David

As ours is.

There is no excuse for frozen condensate pipes. Condensing boilers are used in many countries with worse cold spells than ours.

What diameter is the condensate pipe? I believe 32mm is recommended where freezing is possible. You can allways fit a pipe heater under the insulation. You would obviously use a self regulating type connected to a frost stat so it's not on all the time.

http://www.tlc-direct.co.uk/Main_Index/Cable_Accessories_Index/Heat_Tape/index.html

Thanks for heat tape reference. External pipe is less than 32mm and boiler instructions do indeed state that "condensate should, if possible, be discharged into the household internal drainage system. If this is not practicable, discharge can be allowed into the external household drains . . .it is recommended that any external condensate drain pipe is insulated and also preferably of 32mm diameter to prevent freezing . . ." Looks like yet another area where householder has to read, interpret and enforce instructions rather than trusting "experts" to get on with the job. Question remains, how many installers, country-wide, have ignored this advice and how many will continue to do so under new boiler scrappage scheme?

I know two people who've had this problem during the past fortnight but I get the impression there is a big issue related to the workmanship associated with installing some of the new boilers and some of the installers are inadequately trained (being corgi registered doesn't mean you know how to install all the new stuff). There could also be an element of wanting to get the job finished, i.e. its easier to put the pipe outside than to link it to the internal waste pipe.

Trouble is when householders get the problem it is them who have to pay to get it corrected.

New boilers and installation ought to be covered for five years against things going wrong providing servicing is maintained annually. This would tighten up the profession and would also make ******* *** (= large gas company) actually keep to their servicing schedules (rather than allowing them to slip a couple of months every year, which of course means they make more money.

Interesting idea. Perhaps slightly harder to insulate?

Posted By: beelbeebubHowever we did note that fitting a T peice instead of an elbow where the pipe emerges from the wall would allow a vertical "stub" with a loose fitting cap. Normally this will not cause a problem, however should the pipe freeze (it is likely to freeze away from the elbow as the condensate is warmer when it emerges from the building and won't freeze immediatly) the excess will overflow initally preventing the back flow issue (or at least delaying it). Once the over flow does freeze and the boiler stops working, diagnosing the problem shoudl be easier as the frozen water sticking out of the overflow will be a giveaway. The stub then offers a convenient point oto pour hot water down the pipe.

The additional cost should be minimal (the cost differntial between an elbow and a T, plus the price of a cap, say a normal blanking peice with notches cut around the edge)

Any comments on this proposal?

The condensate is acidic, albeit no more so than tomato juice, but the discharge methods are regulated and all measures should be taken to avoid condensate coming into contact with or discharging onto a person/s skin. Not sure your method is safe if it backs up and spills out over someone stood below.

Our boiler is on the outside wall of the garage. Routing it to any internal drain would either mean pumping it up and across the ceiling or digging up the floor. So I'm not surprised it was connected to the nearest outside downpipe. In colder climates or in a new build it would make sense to arrange an internal run.

I believe condensing boilers have internal traps on the condensate drain.

Posted By: David OlivierIMO installing a boiler far away from the house e.g. on other side of garage is a design failure.

Indeed so. I should perhaps add that our garage is integrated within the house. That's a design failure of a different type by a person or persons unknown nearly 40 years ago.

Thanks for resurrecting this, Dominic.

Hadn't heard of the flooding problem, always thought the boiler would close down once the condensate drain pipe had frozen.

The idiot who fitted our boiler used 22mm overflow pipe (despite Worcester/Bosch advising 32mm - wish I'd known that at the time) through the wall and took it down to the soakaway below. The boiler shut down two years ago, the winter of its fitting, and we called him out to fix it (I had no idea of the condensate drain pipe problem then). He didn't charge us for the call-out. The pipe had frozen to the drain cover so he cut it off about a metre up the wall and used a length of 50mm soil pipe which he clamped to the wall with the drain pipe inside it. Last winter the boiler stopped working and I immediately checked the drain pipe. Inside the 50mm pipe was a solid core of ice!

I cut the 22mm drain pipe down to a length of 300mm and left it like that, hanging there but dripping well clear of the wall. We've had a week of zero temperatures 24/7 with lows down to -8C and the (unlagged) drain pipe is still dripping freely (I suspect because the run is now so short that the water is still warmish). Once the damn builder returns to finish off the pointing and other work on that side of the building I can re-site the pipe against the wall and build a treated-wood box cover to hide the drain pipe and gas supply pipe on the wall.

Oh, and those of you who remember the post about the tree-root-blocked soakaway pipe a couple of months ago - that's when the builder was supposed to have done the pointing work!

Posted By: djhI've no idea *how* the outlet became blocked but it didn't cost anything extra to fix so I had no motivation to question it.

We had a similar problem during our boiler's first few months of service. I found that the blockage could cleared by squeezing the flexible condensate drain hose. The engineer told me that during the first heating season the acid in the condensate cleans all the maufacturing gunk, grease, etc off the heat exchanger & this solution can be sticky, causing the condensate ball valve to stick to its seat.

David

To clarify: if the boiler has its own trap, like djh's, are you suggesting we fit a second one? If so, should it be sealed, or open to the room like the typical washing machine trap?

Can't speak for all condensing boiler types but with many that use a syphonic trap arrangement, if you incorporate a second trap into the condensate discharge line then you will likely worsen the problem as this will prevent syphonic action taking place.

Thanks Dantenz - if I understand correctly you need an air gap to ensure atmospheric pressure downstream of the first trap, and upstream of the second trap. Otherwise the two traps would interfere with each other.

Beyond that, I suspect the answer for any given boiler is to Read The Friendly Manual.

Just to add to this running internally only works if you are going to an internal stack. We had a blockage where the condensate ran to a sink drain, but the sink drain ran to an external gully via a short external stub (~200mm) in 50mm push fit. the external portion froze and blocked the sink. Luckily it was relatively easy to clear as the external push fit was disassembled, a hot air gun used to melt the ice a little then hot water run down the sink to clear the blockage.

At a separate site we now use 32mm pushfit, insulated, with a blanked off "T" connector instead of an elbow at the top. When that blocked we were able to remove the lower, iced, portion, chuck it in a shower to clear and also pour hot water down the pipe from the "T" to clear any residual ice.