Boiler Stopped in Freezing Weather? Check the Condensate Pipe

In short

If your combi or condensing boiler stops in freezing weather, a frozen condensate pipe is one of the most common causes. Thaw it with warm (not boiling) water, then reset the boiler once as your manual describes. If it stops again, or you are unsure, call an engineer.

On this page

• What a condensate pipe does
• Signs it has frozen
• How to thaw it safely
• What not to do
• Stopping it happening again
• When to call Adrian
• Frequently asked questions

What does a condensate pipe do?

A condensing boiler turns the gases it burns into heat very efficiently. As part of that, it produces acidic water (condensate) that has to drain away. The condensate pipe carries it from the boiler to an outside drain. It is usually a white or grey plastic pipe, and part of it often runs along an outside wall.

In a hard frost, the water inside that pipe can freeze. A blocked pipe makes the boiler shut itself down as a safety measure, according to Which?. That is why the heating and hot water can cut out on the coldest mornings, even though nothing is broken.

Signs the condensate pipe may have frozen

• The boiler stops working during or just after freezing weather.
• The boiler shows a fault or lockout on the display. The code differs by make, so check your manual and write the code down.
• You hear gurgling from the boiler or pipe, or the heating and hot water have both stopped.
• The outside section of white or grey pipe is cold, and you can see ice at the end or at a bend.

These signs can also have other causes, including low pressure. If you are not sure, our guides on boiler pressure dropping and heating not working but hot water is cover other common causes.

How to thaw it safely

This only involves the plastic pipe outside the boiler. It does not involve opening the boiler or touching any gas parts.

1. Find the pipe. Follow the white or grey plastic pipe from the bottom of the boiler to where it goes outside or into a drain.
2. Use warm water, not boiling. Fill a watering can or jug with warm tap water, or let a kettle cool for a few minutes. Pour it slowly over the frozen section. A warm (not hot) cloth or hot water bottle held against the pipe also works.
3. Work from the top of the pipe down. Councils advise this can take up to 30 minutes in some cases.
4. Reset the boiler once. Follow the reset instructions in your manufacturer's manual. Do not keep pressing reset.
5. Check it is working. If the boiler fires up and the heating comes back, keep an eye on it over the next day.

What not to do

• Do not use boiling water. It can crack the plastic pipe or fittings, which turns a small problem into a leak.
• Do not open the boiler casing or try to clear the condensate trap inside the boiler. That is a job for a Gas Safe registered engineer.
• Do not keep resetting the boiler. Repeated resets will not clear a frozen pipe and can hide another fault.
• Do not climb ladders in icy conditions to reach a high pipe.

Stopping it happening again

Advice from Which? is that the best protection is to keep as much of the pipe indoors as possible and insulate any part that has to run outside. Moving or re-routing the pipe, or fitting trace heating, is not a DIY job and needs a heating engineer. A Gas Safe registered engineer must fit trace heating. If you have an annual service booked, you can ask the engineer whether your pipe could be re-routed or made larger. Our guide to the best time to service your boiler explains why a service before the cold weather helps.

When to call Adrian

Call an engineer if:

• the boiler stops again after you have thawed the pipe and reset it once
• the pipe will not thaw, or you cannot reach it safely
• there is a leak, a split pipe or water where it should not be
• you can smell gas or suspect carbon monoxide (follow the safety box below)
• you are not sure whether the pipe is the problem

Adrian offers emergency call-outs for urgent plumbing and heating problems. You can read more about our boiler repair service. Adrian will talk through the problem and agree the next step, and a free quote is available if a repair is needed. Adrian Plumbing & Heating is Gas Safe registered (registration number 563742) and rated 5.0 on Google.

Call Adrian on 07899 728506 or request a callback at adrianplumbingandheating.co.uk

Disclaimer: This article provides general guidance only. Always follow your appliance manufacturer's instructions and use an appropriately qualified professional for gas, electrical and plumbing work. Gas work must be carried out by a Gas Safe registered engineer.