How to thaw a condensate pipe

What is a condensate pipe?

A condensate pipe carries condensation from your boiler to your outside drain. It’s usually a white or grey plastic pipe that travels from your boiler through the wall directly outside where your boiler is located.

During cold weather, the condensation in this pipe may freeze and cause a blockage causing the condensation to back up into the boiler and cause it to shut down.

How to tell if a condensate pipe is frozen

If your boiler condensate pipe is frozen there will usually be a few tell-tale signs:

• You may hear gurgling noises coming from your heating system
• Your boiler has shut off or ‘locked out’ during freezing temperatures (though there could also be other reasons for this)
• Your boiler is displaying a specific fault code on its display

Frozen condensate pipe fault codes

The fault code you see on your boiler if you have a frozen condensate pipe will depend on which brand of boiler you have. You can usually find a list of boiler fault codes either in you boiler manual or online from the boiler manufacturers website.

We’ve listed some popular brands and their specific fault codes below. Always check your boiler manual to double check the fault code for your specific model.

How to defrost or thaw a condensate pipe

Step 1: Confirm the condensate pipe is frozen

Depending on the make and model of your boiler, a frozen condensate pipe may be indicated by a ‘fault code’ or warning light on the boiler’s display. Gurgling or bubbling sounds coming from the boiler or the condensate pipe are another sign that the condensate pipe has frozen.

Step 2: Locate the blockage

The pipe is probably frozen at its most exposed point. This may be the open end of the pipe, or at a bend or elbow. Running your hands over the pipe until you find a section that feels colder than the rest should help you identify the blockage quickly.

Most condensate pipes freeze near to the ground, so it’s simply a case of pouring the hot water over the pipe slowly.

Step 3: Use a hot water bottle to thaw the pipe

The best way to thaw your condensate pipe is to apply hot towels or a hot water bottle to the frozen part of the pipe.

First, boil some water. If you don’t have a hot water bottle and are using hot towels instead, make sure to cool the kettle for at least 15 minutes once it’s boiled. Do not use boiling water as you’ll need to handle the towel safely.

Fill a hot water bottle or soak the towel and press them against the frozen blockage in your condensate pipe until it melts. Repeat the process if necessary.

Top tip: If the temperature is around -2 degrees or lower then water can freeze quickly. If you’ve used the towel method, be careful not to slip on any drips that might have frozen.

Step 4: Reset your boiler

Once the frozen section has been melted and cleared, check your boiler manual for instructions on how to reset the boiler correctly. Your boiler should now restart.

Step 5: Not fixed? Keep trying

It may take several attempts before your boiler restarts, but if it doesn’t, you may need to call out a qualified boiler engineer.

How to stop your condensate pipe from freezing

It’s easy to thaw your condensate pipe once it has frozen, but it’s better to prevent your pipes from freezing in the first place. We asked Home Expert Chris for tips on how to stop your condensate pipe freezing, and save you the hassle of waking up to no hot water.

Wrap it in some old towels

If your condensate pipe isn’t already insulated, wrap it in some old towels immediately to prevent it freezing.

Get foam pipe insulation

As soon as you can, get down to your local DIY store and buy some foam pipe insulation to wrap the condensate pipe in (just make sure to check it’s for external use). This insulation comes in a variety of sizes, so measure the pipe’s diameter before you buy.

Turn up the heat!

During extreme weather conditions, even proper insulation may not be enough to prevent the condensate pipe from freezing. It may help to temporarily run your boiler with the boiler thermostat set as high as possible for as long as the cold spell lasts. But if you continue to experience problems, it’s best to call out a qualified boiler engineer for help.

Cover your drain opening

Add a leaf guard over the open end of your drain to remove any wind chill. This will reduce the chance the water in your condensation pipe is exposed to sudden drops in temperature—meaning it’s less likely to freeze.

Boiler still not working?

If you’ve followed our advice on how to thaw a condensate pipe but your boiler still isn’t working, try diagnosing your central heating problems. Alternatively, you may need to call out a qualified boiler engineer.

HomeServe’s nationwide network of Gas Safe engineers are here to help. Simply get in touch, safe in the knowledge you can count on us to keep you feeling toasty this winter.

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