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PLUMMETING temperatures and long periods of sub-zero weather can cause your boiler to stall, just when you need it most to give you heating and hot water.

Nine times out of ten, if your boiler has shut down during icy conditions, it will be due to a frozen condensate pipe. Sorry to say, no attempt to re-fire your boiler will work until your condensate pipe has been properly thawed.

But if you read on you’ll find all the correct advice to ensure you can thaw your condensate pipe thoroughly, without causing damage to your home or heating system.

You’ll also find a few tips so you can avoid the same problem cropping up again.

Nothing is worse than realising your heating system gave up on you hours ago and you’re now in the cold grip of winter. No amount of prodding and pressing buttons on your boiler will bring it back to life if you have a frozen condensate pipe.

It won’t be possible to restart your boiler until you have fully thawed your frozen condensate pipe. You must first clear the blockage of frozen waste water that built up gradually from a trickle until your condensate pipe became packed with ice.


An extended period of sub-zero temperature will be your first clue to diagnosing a frozen condensate pipe. If your condensate pipe has frozen, your boiler may make unfamiliar gurgling or coughing noises. Your appliance’s control panel may also be showing a fault code or error sign as it has detected a blockage and shut down to prevent damage to the boiler.


When boilers are working correctly they create by-product water known as condensate. Condensate is removed from the boiler via a condensate pipe, which is usually a plastic white pipe exiting your boiler from the centre and bottom of the appliance. From there it continues internally, or exits your property through an external wall, and runs along the wall at a steep angle until it reaches a drain or rainwater hopper head.


In the unlikely case your frozen condensate pipe has been insulated, remove all lagging from the pipe before beginning the thawing process. Prepare some warm water by boiling a kettle and mixing it two parts to one of cold tap water in a mixing jug. Pour your warm water over the sections of the pipe which feel coldest to touch, as these will be the most blocked areas of the pipe. Repeat the exercise ensuring also to pour warm water on any flat sections or elbows in the pipe as these typically freeze more quickly. If this method fails to clear the blockage press a hot water bottle filled with near boiling water to the coldest sections of the pipe for extended periods to ensure any packed ice melts completely.

Do Not

  • Pour boiling water directly onto the pipe as this can cause it to crack and presents a hazard for you in icy, slippery conditions.
  • Cut or remove the boiler condensate pipe as this is part of your boiler’s flue system and should only be worked on by a Gas Safe engineer.
  • Let the water you pour gather on pathways where it can freeze and present hazards for you and others later on.


Once you have seen water and ice leaving the pipe and believe the blockage has melted, replace any insulation and lagging on the condensate pipe. Reset your boiler according to its manufacturer’s instructions found in their user manual which was left with you by your Cosy Abodes engineer. If you find the guidelines difficult to follow or can’t find them at all please call Cosy Abodes and one of our engineers will talk you through the process.


The following tips will help you avoid all the unnecessary hassle associated with a frozen boiler condensate pipe:

  • Insulate your condensate pipe with waterproof lagging. Cosy Abodes recommends ‘Armaflex Tuffcoat’ which can be easily sourced online or from most reputable hardware stores.
  • Inspect and clear any build-up of moss in your drain, rainwater hopper head or inside the end of your condensate pipe. Moss restricts the outflow of condensate and grows quickly in these places due to the warmth of water leaving your boiler.
  • Ask Cosy Abodes to move your condensate pipe internally to an area which never falls below room temperature.
  • Ask Cosy Abodes to increase the fall angle of your condensate pipe to improve flow and reduce the likelihood of freezing and blockage.
  • If you have a 22mm condensate pipe, ask Cosy Abodes to replace it with a 32mm condensate pipe to improve flow and reduce the risk of freezing and blockage.