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Frozen condensate pipe? How to thaw it and get your boiler back on
If your boiler stopped on a freezing morning and it’s gurgling or showing a fault, the small plastic pipe outside is usually to blame. You can often sort it yourself with warm water and a reset.
- 4steps to thaw it safely
- 0boiling water, ever
- £120repair visit if it still won’t start
4steps to fix it
Every year the first hard frost in Fife brings the same calls. The boiler was fine last night, and this morning there’s no heating, no hot water and maybe a gurgling noise from the kitchen.
Most of the time it’s a frozen condensate pipe. The good news is that it’s one of the few boiler problems you can usually fix yourself, safely, without waiting for an engineer.
Here’s how to tell if that’s what’s happened, how to thaw it, and how to stop it happening again.
What is a condensate pipe?
Nearly every modern gas boiler has one.
Modern boilers are condensing boilers. They squeeze extra heat out of the flue gases, and that turns some of the water vapour in them into water, called condensate. It’s slightly acidic, so it can’t stay in the boiler. A plastic pipe carries it away to a drain.
When that pipe runs outside, the water sitting in it can freeze in a cold snap. Once it’s blocked, the condensate backs up and the boiler shuts itself down to protect itself. Nothing is broken. It’s a safety lockout.
How do I know it’s frozen?
- It’s been below freezing, often overnight
- The boiler has stopped and shows a fault or lockout
- You can hear gurgling from the boiler
- There’s ice in or at the end of the pipe outside
The fault code depends on the make. Worcester Bosch boilers may show an EA code, and Vaillant boilers F28 or F29. Our boiler fault code guide covers the main makes.
Condensing boiler
How to thaw it
Four steps, and no tools needed.
Find the pipe
Follow the white or grey plastic pipe from under the boiler to where it leaves the house. It usually runs down the outside wall into a drain or gully. It tends to freeze at the open end or at a bend, where it’s most exposed.
Warm it up
Pour warm water slowly along the pipe, working towards the open end. A watering can or a kettle that’s been left to cool is ideal. A hot water bottle or a microwave heat pack held against the pipe works too. Never use boiling water.
Reset the boiler
Once the ice clears and water drains out, press the reset button or follow the reset steps in your manual. If it locks out again straight away, give it a few minutes and try once more.
Watch your step
The water you pour can freeze on the path, so put down some salt or grit afterwards. Keep an eye on the boiler for the rest of the day, especially if the frost is set to carry on overnight.
Don’t take risks
If the pipe is high up the wall, don’t get the ladders out on ice. Give us a call instead. And if the boiler still won’t reset after the pipe is clear, stop resetting it and book a repair.
Stopping it happening again
If yours freezes every winter, it can be sorted.
In a really cold spell, you can turn the boiler’s heating temperature up for a few days. It makes less condensate, which lowers the chance of a freeze. Turn it back down when the cold snap is over, because lower is cheaper to run the rest of the year.
For a permanent fix, the options are:
- Rerouting the pipe inside to a waste pipe, which is the preferred method
- Making the outside run as short as possible
- Fitting a wider pipe outside, which takes longer to freeze solid
- Insulating the outside section
Which one suits depends on where your boiler is and where the drains are. If your pipe has frozen before, mention it when you book your next service and the engineer will look at the options with you.
Reset and check
Still no heating?
- It reset and it’s runningYou’re sorted
Keep an eye on it while the frost lasts.
- It won’t reset, or keeps locking outBook a repair visit
£120 including VAT, before any parts.
- It freezes every winterAsk about rerouting
We’ll look at moving or protecting the pipe.
- You’re on Home Care Boiler or CompleteBoiler repairs included
Call us and tell us you’re a member.
Common questions
Can I use boiling water on a frozen condensate pipe?
No. Boiling water can crack or split the plastic pipe, and you risk scalding yourself. Warm water from a watering can, a hot water bottle or a microwave heat pack is all you need.
Why is my boiler gurgling in cold weather?
Gurgling in a cold snap usually means the condensate pipe is frozen and the water is backing up inside the boiler. Thaw the pipe outside, then reset the boiler.
Will a frozen condensate pipe damage my boiler?
Usually not. The boiler shuts itself down before any harm is done. Once the pipe is clear and the boiler is reset, it should work normally.
Is it safe to keep resetting my boiler?
A couple of resets is fine. If it keeps locking out after the pipe is clear, stop. Repeated lockouts can mean a different fault, and that needs a Gas Safe registered engineer.
Can the condensate pipe be moved inside?
Often, yes. Running it to an internal waste pipe is the preferred method and stops it freezing. It depends on where the boiler sits and where the nearest waste pipe is, so we’d look at it on a visit.
How much is a repair visit if I can’t fix it?
A repair visit is £120 including VAT, before any parts, and we quote for parts before fitting them. On the Home Care Boiler and Complete plans, boiler repairs are included.
Related pages
Sources: Worcester Bosch, frozen condensate advice; Heating and Hotwater Industry Council leaflet on frozen condensate. Checked 1 November 2026.
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