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How to Thaw a Frozen Condensate Pipe

Is your condensate pipe frozen? Here’s our advice on how you can safely defrost your condensate pipe and what you need to do to prevent it from freezing in the future. 

If your condensate pipe is outside, it will likely freeze during the cold winter months and cause problems for your boiler. The good news is that you can fix a frozen condensate pipe yourself without needing to arrange a visit from your boiler engineer. 

Read on to discover how to find and thaw your condensate pipe and what you can do to help stop it from freezing again. 

What is a condensate pipe?

A condensing boiler requires a condensate pipe to transfer the excess water or condensation from your boiler to a drain outside. It extracts heat from the water vapour in exhaust gasses by passing the gasses through a condenser, and the condensed water vapour then exits the boiler through the condensate pipe.

Your gas boiler will likely be a highly efficient condensing boiler if you got it installed in the last 15 years. If you haven’t replaced your boiler after 10 to 15 years, you should look into replacing it, even if it’s still performing well. 

Where is the condensate pipe on my boiler?

The condensate pipe is the only plastic pipe connected to your condensing boiler and is usually a white or grey pipe, similar to the one you may find on your washing machine. All the other pipes are metal pipes, so your condensate pipe should be easy to spot. 

Your condensate pipe will usually be underneath your boiler and lead outside through the wall and into an external drain. The plastic condensate pipe should leave your home through the wall directly by your boiler. When the condensation in your outside condensate pipe freezes, it can cause a blockage and make your boiler shut down. 

In some cases, the condensate pipe will run from the boiler to a drain under a sink. If your condensate pipe runs through your garage or an unheated outbuilding, it can also freeze in cold weather.  

How will I know if my condensate pipe is frozen?

In most cases, your condensing boiler will display a fault code if the condensate pipe is frozen. The user manual that came with your boiler will include a list of fault codes and their meanings to make it easy for you to determine whether your condensate pipe is frozen. 

If your heating system is making unusual gurgling noises or your boiler isn’t performing as it should when a cold snap hits, it may be trying to tell you that your condensate pipe is frozen. You may even find that your boiler shuts down to protect your system and prevent any damage.   

How do I thaw my frozen condensate pipe?

You can defrost your condensate pipe yourself without contacting your boiler engineer. The ground outside by your condensate pipe could be a slip hazard, so be careful when you head out to locate and thaw the frozen blockage. 

Below is our step by step guide on how to safely thaw your frozen condensate pipe.

Step 1: Locate the blockage

The most exposed part of the condensate pipe (on the outside wall) can often freeze during the winter, especially at the bends or dips. You’ll need to feel the condensate pipe with your hands to locate the blockage.

Step 2: Thaw the frozen part of the condensate pipe 

Once you find the blockage, hold a hot water bottle or microwavable heat pack on the frozen section of the condensate pipe until it unfreezes. Alternatively, you can pour warm water onto the blockage using a watering can. Do not be tempted to use boiling water straight from the kettle because this can damage your pipe. 

Step 3: Restart or reset your boiler

After thawing your condensate pipe, you need to restart or reset your boiler. Your user manual should include instructions on resetting your boiler and clearing the fault code should one appear. If the fault code continues to show or your boiler won’t restart, you may need to repeat the above process to clear the blockage. 

You should contact a Gas Safe registered engineer to visit your home and get to the bottom of the problem if repeating the process doesn’t work.

Can I prevent my condensate pipe from freezing again?

Yes, you can follow some simple steps to minimise the risk of a frozen condensate pipe, such as:

Insulate your condensate pipe

Your local DIY store should sell pipe insulation or pipe lagging that you can use to insulate your condensate pipe and protect it from the cold weather. You can insulate your condensate pipe if you feel comfortable doing so, or call a heating engineer to do it for you. 

Install a trace heater

A trace heater is a heating kit that you can use to prevent the water in your condensate pipe from freezing. It requires running a cable alongside your condensate pipe, which heats up whenever it detects a risk of freezing. 

Ask an engineer to move your condensate pipe

If it’s possible to do so, you can ask a Gas Safe registered engineer to move the pipe from outside and make it run internally. Moving the condensate pipe inside won’t be an appropriate solution for every home, but you can ask an engineer whether this is a possibility. 

Leave your heating on low all night

You can keep your heating on low when you go to bed at night during the coldest months of the year to keep your pipe warm and avoid a blockage. 

Turn the boiler thermostat to maximum

Turning your boiler thermostat to the maximum temperature will increase the temperature of your condensate pipe and help stop it from freezing. But be aware that your radiators will be hot when you raise the temperature. Also, keep in mind that increasing the temperature of your heating system will lead to a more expensive heating bill.