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How to Stop Condensate Pipe Freezing

How to Stop Condensate Pipe Freezing in a Cold Winter

Last updated on April 12th, 2024

Learning how to stop a condensate pipe freezing could save you a lot of time defrosting it, or money calling someone out.

A broken down boiler in the freezing winter is a nightmare and often easily preventable.

I have been a full-time heating engineer for over a decade and fixing boilers because of a frozen condensate pipe is very common in sub-zero temperatures.

In this post, I’ll go through what you can do to prevent your condensate pipe from freezing based on my experiences and research.

How to Stop Condensate Pipe Freezing

If you have a condensing boiler, you will have a plastic condensate pipe which is used to get rid of the acidic wastewater that the boiler produces.

This water is created from the vapour after reusing the excess heat to make the boiler more energy efficient.

Condensate pipe under boiler
White condensate pipe under boiler

Condensate pipes should ideally discharge inside the property when a boiler is fitted, and every precaution taken to ensure it doesn’t freeze in a cold winter.

If the condensate pipe gets blocked or frozen, the boiler will cut out and won’t work again until the pipe is defrosted or unblocked.

Internal Gravity Discharge Point

The absolute best way to stop a condensate pipe from freezing is to have the pipe discharge into a soil stack pipe or waste pipe inside the property.

This works with gravity so the condensate pipe must go down on a fall from the boiler to the waste. A toilet soil stack is the best choice but it could go into a sink, bath, shower, or washing machine waste pipe.

Condensate Pump

If you can’t get the pipe to fall from the boiler to the waste (because of doors etc.), you can fit a condensate pump under the boiler and the wastewater will discharge into that.

The condensate pump will then have a tube running to an internal waste so the wastewater can be pumped up and across to wherever it needs to be in the property.

This pump works with a float valve mechanism which automatically pumps the water away when it's full, and is wired to the boiler in a way that will shut the boiler down if it can't pump the wastewater away.

External Condensate Pipe Frost Protection

Sometimes there’s no choice but to run the boiler condensate pipe outside, and often times it’s done because it’s just the easiest option.

They are also often not fitted correctly, even by qualified gas engineers.

Condensate pipe gets bigger
Condensate pipe going outisde

Fitting External Pipe

Any condensate pipe fitted in an unheated area inside the property, like lofts, basements and garages, should be treated as an external pipe.

If fitting a condensate pipe outside, make sure:

  • It is run inside the property as much as possible before going outside
  • It is at least 30mm internal diameter and goes all the way through the wall in this size
  • There are no horizontal sections outside, keep it as vertical as possible
  • The end of the pipe terminates below the grating level but above the water level

Protecting External Pipe

You should take condensate pipe frost protection seriously, especially if it has frozen before.

How to stop your external condensate pipe freezing:

  • Fit a Drain Cover
  • Fit Pipe Insulation
  • Fit a Trace Heating Kit

Drain Cover

Fitting a drain cover or leaf guard over the end of the condensate pipe is a simple way to help protect against wind chill freezing it.

Drain cover frost protection
Drain cover frost protection

Insulate External Pipe

Insulate every piece of condensate pipe outside the house with external pipe insulation. This will help greatly in those freezing temperatures.

The thicker and better quality insulation you use the better. This should be sealed to the wall and every connection sealed as good as you can get it. This is to ensure it protects from freezing the best it can.

Thick insulated condensate pipe
Insulated condensate pipe

It’s typically undersized (22mm) horizontal pipes that freeze, but you can insulate any external condensate pipe, especially if it has frozen before.

My recommended condensate pipe insulation on Amazon:

Insulated condensate pipe
Insulated undersized condensate pipe

Trace Heating Cable

Fitting a trace heating cable is a great way to stop your boiler condensate pipe from freezing an external pipe. It uses a self-regulating cable to heat the pipe when it drops below a specific temperature.

This will keep the pipe warm and is the best way to stop an external condensate pipe from freezing in the winter.


The ideal way to prevent condensate pipes from freezing is to fit them according to the HHIC guidelines but often you will have undersized external pipes fitted horizontally.

White condensate pipe
White condensate pipe

This is how the majority of frozen condensate pipes happen in the winter and if you don’t want to upgrade or reroute the pipe, you can fit a drain cover, insulate the pipe and fit a trace heating kit to give it the maximum frost protection.

You can also fit a Worcester CondensSure to your condensate pipe which keeps the wastewater warm but I’ve never tried them.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you find it helpful.


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

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