A lesson learnt, the hard way!

  canarieslover 10:06 05 Mar 2018

About 16 months ago I had to have a new boiler fitted. Of course they fitted a condensing boiler as these are the modern standard. I asked at the time whether I needed to lag the condensate pipe where it ran outside the house and the answer was "No, it's 32mm pipe and the condensate is not great so it won't freeze up." Last week the inevitable happened, it froze. I didn't realise at first but I did notice the boiler making the occasional gurgling noise. On Saturday I was clearing the snow along the back of the house when I noticed an inch of ice protruding from the bottom of the pipe so I got a kettle of hot water to thaw the angle section to the drain. after several kettles I managed to remove a piece of ice 25cm long 32mm diameter. That didn't cure the problem so I cut the pipe off near the elbow where it came out of the wall and discovered it was still solid there. I thawed that out and got a new length of pipe to cure the problem. I then searched for 32mm pipe insulation with no luck so I improvised with 22mm and now I have a pipe that shouldn't freeze again. Searching on line for advice it seems that it is only recommended that you insulate pipes with greater than a 2 metre run and mine was only 1.5 metres. Lesson now learnt !!!

  LastChip 10:55 05 Mar 2018

That's worth knowing canarieslover, as most of us that have had new boilers fitted in the last few years, will almost certainly be condensating boilers and I've yet to see one with the condensate pipe lagged.

That said, it could be related as to how much of the run is of a horizontal nature. My own pipe is almost vertically down and straight into the drain and I didn't have any issues with it last week.

And, although severe by local standards, we didn't suffer anywhere near as bad as the north of the country.

  rickf 11:08 05 Mar 2018

I understand that the said pipe should be directed to an outlet internally and not outside. It's standard procedure in Europe I believe. Mine is directed internally to an outlet under the bath. Fitter did this last year and said it should always be the case if possible.

  canarieslover 11:12 05 Mar 2018

LastChip - Mine is about 30 degrees from vertical with a short section to the drain that is around 35 degrees from parallel to the ground. I have looked at neighbours installations and none of those are lagged either.

  Forum Editor 11:15 05 Mar 2018

There is only one absolutely guaranteed way to stop a condensate pipe from freezing up, and that is to fit a thermostatically controlled trace heater.

Otherwise, try to re-route the pipe so as much of it as possible is inside the house, alter the run so the external part is as near vertical as possible, change the external section to black pipe (if it gets any exposure to sunlight), and insulate it.

  Forum Editor 11:18 05 Mar 2018


Current regulations allow the condensate pipe to run internally or externally. Most fitters seem to opt for the external method, probably because it is almost always easier and quicker.

  Belatucadrus 11:38 05 Mar 2018

Ours froze the first year it was fitted, so dad added a T section with a cap so we could pour boiling water in it. As soon as the snow cleared I double lagged it with an initial layer of metalised bubble wrap then put foam pipe lagging over that. It hasn't frozen since.

  rickf 12:44 05 Mar 2018

"Most fitters seem to opt for the external method, probably because it is almost always easier and quicker." And I think that is the case, cutting corners to save time and maximize profit or pure laziness. The fitter I had was excellent. He had taken the trouble to take out the side panel of the bath and installed the pipe from the boiler to an outlet next to the waste pipe. Difference between someone who is conscientious and a "cowboy". He also explained that there had been occasions when fitting it internally was impossible for obvious reasons so that the external option is employed, but always as a last resort.

  Forum Editor 14:45 05 Mar 2018


I wouldn't describe someone who fits an external condensate pipe as a cowboy. That method is perfectly permissible under the current regulations.

  rickf 14:52 05 Mar 2018

that method is perfectly permissible under the current regulations. Lots of things and methods are approved by regulations. Doesn't necessarily mean its the correct way. How about Grenfell claddings??

  john bunyan 14:55 05 Mar 2018

If the boiler condensate goes into the bath waste, does that outlet have to be lagged , assuming that in some cases, the bath outlet joins an external soil pipe. Clearly a good idea if the soil pipe is internal and accessible to the boiler. I have yet to switch to a condensing boiler but my regular boiler man says he would lag an external pipe if I had one.

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