If your boiler has stopped in cold weather and is making a gurgling or bubbling noise, the most likely cause is a frozen condensate pipe. This is one of the few winter boiler faults you can usually fix yourself.

What the condensate pipe does

A condensing boiler produces slightly acidic water as a by-product and drains it away through a plastic pipe, usually about 22mm, that runs outside to a drain or soakaway. If that pipe freezes, the water backs up, the boiler detects it and shuts down.

How to tell it is the condensate

• It happened during or just after a cold snap
• There is a gurgling or bubbling noise from the boiler
• There is a white plastic pipe running out through the wall near the boiler
• It locks out again shortly after every reset

How to thaw it

1. Find where the pipe runs outside. The freeze is usually at a bend, at the open end, or anywhere it runs exposed.
2. Warm the pipe with a hot water bottle, a microwaveable heat pack, or a cloth soaked in warm water held against it.
3. Work along the pipe rather than at one spot.
4. When it clears you may hear water run. Reset the boiler.

If it keeps happening

A pipe that freezes every winter is usually undersized, poorly routed with too many external bends, or uninsulated. The permanent answers are lagging it, increasing the diameter of the external run, re-routing it internally, or fitting a trace heating element. Any of those is a short job and it stops the problem returning every year.

When to call someone

If you cannot reach the pipe safely, if thawing does not clear it, or if the boiler locks out for a different reason once the pipe is clear.

Frequently asked questions

Can I pour boiling water on it?

No. Warm, not boiling. Boiling water can crack the pipe and scald you.

Why does it only happen in winter?

The pipe carries water and freezes when the external temperature drops below zero for long enough.

How do I stop it happening again?

Lagging, a larger external pipe, an internal route, or trace heating. All are short jobs.

Is it covered by my boiler warranty?

Freezing is usually treated as an installation or maintenance matter rather than an appliance fault. Ask your installer.

Want it sorted properly?

Still stuck? We repair this fault regularly across Hertfordshire, Bedfordshire and Cambridgeshire. Call 01462 506374 to get an engineer booked, or to talk it through first if you would rather. Genuine 24 hour cover, 365 days a year.