It’s the coldest morning of the year, the house is freezing and the boiler has stopped with a fault code. Before you panic, check the small plastic pipe outside. A frozen condensate pipe is one of the most common causes of boiler breakdowns in a cold snap, and it’s often something you can sort yourself with a kettle of warm water. In this post we’ll explain how to spot it, how to thaw it safely, and when to book a boiler repair across South London and Kent instead.
What is a condensate pipe?
Modern condensing boilers produce slightly acidic water as they work. The condensate pipe carries this away, usually to a drain or soakaway. It’s normally white or grey plastic, about 21 to 32mm wide, and often runs out through the wall near the boiler.
When the part outside the house freezes, the water can’t drain. It backs up into the boiler, which shuts down to protect itself.
Signs your condensate pipe has frozen
- The boiler has stopped during freezing weather
- A fault or lockout code is showing on the display
- You can hear a gurgling noise from the boiler
- The outside section of the pipe looks frosty, or you can see ice at the end
Fault codes vary by brand. Our guide to common boiler error codes explains some you might see, and your boiler manual will list the condensate fault for your model.
How to thaw a frozen condensate pipe safely
Only work on the pipe at ground level, and never climb a ladder in icy conditions.
- Find the frozen section. It’s usually at the end of the pipe, at a bend or where it runs along an exposed wall.
- Pour warm water over it. Use a kettle that has cooled for a while, or a watering can of warm water. Never use boiling water, as it can crack the plastic pipe.
- Or hold a hot water bottle or microwavable heat pack against the pipe for a few minutes.
- Keep going until the ice clears. You may hear water start to run.
- Reset the boiler following the manufacturer’s instructions. It may take a few minutes to start up again.
If the boiler won’t restart after a couple of tries, stop and call an engineer. Don’t keep resetting it.
What you shouldn’t do
- Don’t use boiling water on plastic pipework
- Don’t use a blowtorch, heat gun or any naked flame
- Don’t remove the boiler casing or try to clear the trap inside the boiler
- Don’t climb ladders to reach a high pipe in ice or snow
Anything inside the boiler is a job for a Gas Safe registered engineer.
How to stop it happening again
If your condensate pipe freezes every winter, it may not have been installed to current guidance. Common fixes include:
- Lagging the outside section with waterproof, weather-resistant pipe insulation
- Increasing the pipe size outside, as wider pipes are less likely to freeze
- Rerouting it internally, to an internal waste pipe or drain where possible
- Shortening the external run and making sure it falls steadily, with no dips where water sits
These are quick jobs for an engineer and can save you a cold morning every year. A regular service through a boiler care plan is a good time to have the pipe looked at.
Condensate pipes in South London and Kent
Plenty of homes in Bexley, Sidcup, Bromley and Sevenoaks had combi boilers fitted in kitchens on outside walls, with a long plastic pipe running down the outside to a gully. Those runs are the ones that freeze. Flats can be trickier, as the pipe may run along a balcony or a high wall that you can’t reach safely.
Frequently asked questions
Is it safe to use my boiler with a frozen condensate pipe?
The boiler will usually shut itself down, so you won’t be able to use it until the pipe is cleared. That’s a safety feature. Once you’ve thawed the pipe, reset it once or twice. If it still won’t run, call an engineer.
Why won’t my boiler restart after I thawed the pipe?
There may still be ice further along the pipe, or the condensate trap inside the boiler may be blocked. There could also be a separate fault. If two resets don’t work, leave it and book an engineer.
Can I pour boiling water on a frozen condensate pipe?
No. Boiling water can crack or deform the plastic, giving you a leak to deal with as well. Warm water from a kettle that’s been left to cool for a while is much safer.
Will my boiler warranty cover a frozen condensate pipe?
Usually not, as freezing is treated as a weather issue rather than a fault with the boiler. Check your manufacturer’s terms, or ask us when you call.
Boiler still not working?
If you’ve thawed the pipe and the boiler still won’t fire up, give us a call on 020 3722 5095 or drop us a message and we’ll get an engineer out to get your heating back on.