How to defrost a frozen condensate pipe: a step-by-step guide

In the middle of a cold snap, the last thing anyone wants is for their heating to stop working. But on the chilliest of days, even the healthiest boiler can struggle.

Often, this can be the result of common boiler problems that you can fix yourself at home. One such problem is a frozen condensate pipe, which can easily happen on icy winter days.

Here’s our guide to how to spot and thaw a frozen condensate pipe – and how to prevent it from happening again!

What is a condensate pipe?

If you have a condensing boiler, then it will have a condensate pipe. Unless you have a really old boiler, it’s likely that you do – it’s been law in the UK since 2005 that all new boilers must be condensing.

So whatever brand of boiler you have – Worcester, Bosch, Vaillant, Viessman or any other – it probably has a condensate pipe somewhere. Read more about the different types of boiler, and how to figure what yours is, in our handy guide.

What does the condensate pipe do? Well, just as the name suggests, condensing boilers create condensation – and the condensate pipe gets rid of the excess.

Finding your condensate pipe

There’s a simple way to spot which pipe is your condensate pipe: it will be made of plastic, while the other pipes coming from your boiler are more likely to be made of copper or steel. 

Condensate pipes are always made of plastic because the water (or condensate) that the pipe disposes of is mildly acidic. The acid would corrode a metal pipe, so plastic is used to keep it intact.

Condensate pipes often run outside the house and into an external drain, or sometimes into an unheated room of the house (such as a garage). 

Why do condensate pipes freeze?

The condensate pipe usually runs outside of the house, and into a drain. Why does it freeze? Because of the temperature! It’s at extra risk of icing over because it’s braving the elements outdoors.

If you’re battling the cold at home this winter, read our guide to the most efficient way to heat your home, and 10 home hacks to keep the house warm.

How to know if your condensate pipe is frozen

There are three main telltale signs of a frozen condensate pipe.

1. The heating isn’t working. 
2. Your boiler’s making a gurgling or slurping sound.
3. There’s an error code on your boiler display that indicates a problem with the condensate pipe. (See the bottom of this article for more on common condensing pipe error codes.)

If your boiler had been working pretty well up until you were hit with wintry weather, that’s usually a sign your condensate pipe is frozen.

Recognising the signs above? Read on to find out how to thaw your condensate pipe.

Confused by your error code, or still unsure what the problem is with your boiler? Read more about common boiler problems and how to fix them, as well as how to tell if your boiler’s pressure is too low, and how to bleed your radiators. 

A quick guide to how to defrost your frozen condensate pipe

Once you’ve identified the problem, you’ll want to know how to unfreeze a frozen condensate pipe. Here’s our step-by-step guide.

1. Figure out which part of the pipe is frozen. If your pipe goes outside, it’s most likely to be the part that’s exposed. To find the blockage, run your fingers along the pipe – the part that feels coldest is probably frozen.
2. Boil your kettle. Once you’ve done this, wait for 10-15 minutes to let the water cool down. 
3. Pour the kettle water onto your pipe. You can do this along the whole length of the exposed pipe, or if you’ve located the blockage, you could just do it on that spot.

The warmth of the water should melt that troublesome ice. You could also try using a hot water bottle on the blockage, to see if that does the trick. 

Once you’ve done this, reset your boiler to see if the problem’s been solved. If it has, your heating should start up. If not, it may be worth trying again. After a few attempts, if the heating is still not working, you should call a professional to take a look. 

Should you pour boiling, hot, or warm water on a frozen condensate pipe?

Always make sure you wait for 10-15 minutes after boiling water before you pour it on your condensate pipe. Or you could use a hot water bottle, or water from the hot tap.

Never pour boiling water directly on your condensate pipe. You could crack the pipe and cause more damage. The water you use should be warm or hot, but not boiling.

How to prevent your condensate pipe freezing

Want to make sure this doesn’t happen again? Here are some ideas for how to avoid frozen condensate pipes on your boiler.

Reduce the exposure of your condensate pipe

The less pipe is outside, the less pipe can freeze in cold weather. To make changes to the location of your condensate pipe, you’ll have to call an engineer to come and take a look.

Insulate the pipe

To stop the pipe from freezing again, wrap it in some old towels or blankets to keep it cosy. When you get the chance, head to your local DIY shop, and pick up some foam pipe insulation (make sure you measure the pipe’s diameter first!). This type of external condensate pipe insulation can work wonders at protecting your heating from the elements.

If your pipe is difficult to access, call a professional to do this for you.

Change the angle of the pipe

Pipes that point downwards steeply are less likely to have water trapped inside them. The same goes for pipes with fewer bends. This means there’s less likelihood of the pipe freezing. 

To change the angle or the bends of your pipe, you’ll have to get the help of a professional.

Ask your plumber about installing a trace

If you live somewhere that’s regularly very cold, you might need a more serious solution. Ask your boiler installer about fitting a trace – this is an electrical element that can be fitted to your pipe to heat it up when the temperature drops. 

Frozen condensate pipe error codes

Here’s a quick guide to the error codes used by the most common boiler brands, to show that your condenser boiler has a frozen pipe.

If you don’t see your boiler’s error code above, check your boiler manual. Remember, if you’re unsure, you can always call an expert to come and take a look. 

Boiler still not working?

If you’ve tried everything above and your boiler is still playing up, you may need to call an engineer to come and get it running again. 

With OVO Home Plan, you’re always covered in the event that your heating gives up the ghost. Our Boiler and Home Emergency cover starts from just £13 a month¹. That includes unlimited call-outs, and the use of our emergency hotline. Warming up to the idea?

Find out more about OVO Home Plan here

Does your pilot light frequently blow out, or are there sooty stains around any of your gas appliances? This could indicate a carbon monoxide leak. Carbon monoxide poisoning is lethal. Read our guides on how to spot a leak, recognise symptoms of carbon monoxide poisoning, where to place your carbon monoxide detector, and what to do when your alarm goes off. This guide could save your life. 

Sources and references

1  No claims can be made within the first 30 days. Terms, conditions, exclusions and cancellation charges apply. For boilers aged 7 years and over up to £2 a month additional premium will be charged. This product has a £99 excess.