How to thaw a frozen condensate pipe
When it’s freezing outside, lots of boilers stop on the same morning. The usual cause is a frozen condensate pipe. You can often fix it yourself in about 15 minutes, with some warm water.
What the condensate pipe does
Modern gas boilers are “condensing” boilers. They take extra heat out of the hot gases before they go up the flue. This makes them use less gas. It also makes water, which is called condensate.
The boiler drains that water away through a plastic pipe. It’s often white or grey and runs to a drain. If part of the pipe is outside, the water inside can freeze in very cold weather. The water then can’t get out. The boiler senses the blockage and shuts down to stay safe.
Signs your pipe is frozen
- It’s very cold outside, often below zero for a day or more.
- The boiler has stopped, and a reset doesn’t help for long.
- You hear a gurgling or bubbling noise from the boiler.
- The boiler shows a fault code. The code depends on the make:
| Make | Codes to look for |
|---|---|
| Worcester Bosch | EA |
| Vaillant | F.28 or F.29 |
| Glow-worm | F.28 or F.29 |
| Baxi | E133, E119, E128 and others |
| Ideal | L2 or F2 with a gurgling noise. Ideal says this may mean a blockage. |
These codes can also mean other problems, such as no gas. So check the pipe first, then see if the code clears.
How to thaw it
- Turn the boiler off.
- Find the pipe. Follow it from the boiler to where it goes outside. It usually ends at a drain or into the ground.
- Find the frozen part. It’s usually the most open part of the pipe. Look at the open end, at bends, and at any dips where water can sit.
- Warm it slowly. Pour warm water along the pipe from a watering can or jug. You can also hold a hot water bottle or a microwave heat pack on it.
- Never use boiling water. It can crack the plastic pipe. Worcester Bosch, Baxi and Glow-worm all warn about this.
- Repeat until the ice clears and water drains out.
- Turn the boiler back on and press reset. It should start as normal.
Stay safe while you do it. Don’t climb a ladder in icy weather to reach a high pipe. Call an engineer instead. Also, the water you pour can freeze on the ground. Throw some salt or grit down so nobody slips.
How to stop it happening again
Worcester Bosch gives three tips to lower the risk:
- turn the heating control on the boiler up to maximum in very cold weather;
- fit a drain cover to protect the end of the pipe;
- insulate the pipe where it runs outside.
A Gas Safe engineer can lag the pipe or reroute it inside. That’s often a quick job, and it can save a lot of cold mornings.
When to call an engineer
Call a Gas Safe registered engineer if:
- the pipe isn’t frozen but the boiler still won’t start;
- you can’t reach the pipe safely;
- the code keeps coming back after the thaw.
Related guides
If you smell gas, leave the building and call the National Gas Emergency Service on 0800 111 999.