Boiler dead on a frosty morning? Check the condensate pipe first
Updated 1 October 2026 · 2 minute read · From our Gas Safe heating engineers
The first properly cold morning of the year, the house is freezing and the boiler is showing a fault. Before you search for an emergency heating engineer near me, go and look outside. A frozen condensate pipe is the classic January call, and it is often fixable in minutes.
What the condensate pipe does
A modern condensing boiler pulls extra heat out of its flue gases, and that produces water. The water drains away through a plastic pipe, usually about the width of a thumb, that runs out through the wall to a drain or soakaway. If that pipe runs outside for any distance, a hard frost can freeze the water inside it.
When it freezes, the water backs up and the boiler shuts itself down to protect itself. You will usually see a fault code, and sometimes hear a gurgling from the boiler.
How to spot it
- It is below freezing, or has been overnight.
- The boiler was fine yesterday.
- There is a fault code or a flashing light, and a reset does not hold.
- Outside, the plastic pipe from the boiler feels solid, or you can see ice at the open end.
Thawing it safely
- Find where the pipe is most exposed, usually at a bend or at the open end.
- Pour warm water, not boiling, slowly along the pipe. A watering can is ideal. Boiling water can crack plastic pipe.
- A hot water bottle or a warm cloth held on the pipe works too.
- Once it runs freely, reset the boiler following the instructions on the front or in the manual.
Do not try to take the boiler casing off. Everything inside is gas work.
Stopping it happening again
A pipe that freezes every winter is usually too small, too long outside, or has a dip where water sits. The fix is a permanent one: rerouting it inside where possible, upsizing the outside run, or lagging it properly. We check the condensate route and its fall on every boiler service for exactly this reason.
When to call us
If you cannot reach the pipe, it keeps refreezing, or the boiler still will not start once it is clear, ring us. We will talk you through it on the phone first, before charging you for a visit, and in Bridgend county we can usually be with you the same day.
Keep reading
- Cold radiators: how a heating engineer tells bleed, balance and flush apart Where a radiator is cold tells you the fix. Cold at the top, cold at the bottom, or whole rooms never warm: three symptoms, three different jobs, and only one of them needs a powerflush.
- Boiler pressure keeps dropping: how often is too often? Topping up once or twice a year is normal. Weekly is a fault. How to read your pressure gauge, the two usual causes, and why topping up every week costs more than the repair.
- Radiators hot, taps cold: why a combi stops making hot water When a combi boiler heats the radiators but not the taps, the fault is usually one part: the diverter valve. What it does, what to check first, and why it is a repair, not a new boiler.