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Thawing a condensate pipe

When we experience very cold weather many council tenants may find their boilers do not work as a result of frozen condensate pipes.

Ideally the pipe should be thawed out by an engineer from Paynes, but if they can’t get to you because of the weather conditions, here are some easy guidelines to help you sort the problem out yourself.

What is the boiler condensate pipe?

Most modern boilers have a condensate pipe which transports water away from the boiler. To improve efficiency, the boiler removes as much energy from the flues gases as possible and some of this waste gas cools and turns into acidic water.

The condensate pipe transports the water away from the boiler to an internal or external waste pipe or drain. If the condensate pipe freezes your boiler will automatically shut down leaving you without heating and hot water.

There are a couple of ways to tell if your condensate pipe is frozen. You may hear some bubbling sounds coming from the boiler or condensate pipe or there may be a warning light on the boiler indicating the pipe is frozen.

To check if your boiler has a condensate pipe, look underneath it at the pipes. If one of these is plastic (usually white and around 20mm or ¾ inch wide) and the rest are copper you almost certainly have a condensate pipe.

Track the pipe to see if it goes outside – you’ll find the pipe runs to an external waste pipe or drain so the water can run away.

Why does it freeze?

Because the condensate pipe runs outside to a drainage point, during extreme cold weather the water is prone to freezing. This creates a blockage and the water backs up inside the boiler. A switch is activated inside the boiler to shut it down when the water reaches a certain point to prevent the boiler from flooding.

How do I clear it?

It’s recommended that an engineer from Paynes looks at the condensate pipe, especially if you’re unsure of what to do or how to locate the frozen section. But this may not be possible due to the weather conditions and if you feel competent enough to attempt the task yourself there are two methods of thawing out the condensate pipe.

  1. The first method is to remove the lagging if installed and apply hot water (not boiling water as this will crack the pipe) from a suitable container, to the outside of the condensate pipe. If you’re boiler is out of use because of the frozen condensate pipe you can heat the water using a kettle or a microwave. Once the water in the pipe has thawed re-fix the insulation to the pipe to protect it from freezing again.
  2. The second is to remove the lagging if installed and place a hot water bottle on the section where the water has frozen. Once the water in the pipe has thawed re-fix the insulation to the pipe or protect it from freezing again.

You should never attempt to thaw out a condensate pipe that cannot be reached without both feet being on the ground eg off a ladder or try to disconnect it or pull it apart to remove a blockage.

Please employ extreme caution if you attempt to thaw out a condensate pipe. Always use suitable hand protection when handling hot water and be careful not to splash hot water on yourself when pouring it over the condensate pipe.