What is a condensate pipe?
Every modern gas boiler in the UK is a condensing boiler. To be efficient it cools its flue gases enough to turn water vapour back into liquid. That water, called condensate, is mildly acidic and drains away through a plastic pipe. In many Birmingham homes, especially semis and terraces with the boiler on an outside wall, the pipe runs outside to a drain or gully.
Because only a small amount of water trickles through it, the outside section can freeze in a hard frost. Once ice blocks it, condensate backs up into the boiler, which detects the problem and shuts down.
How do you thaw it safely?
- Find the pipe. Follow the plastic pipe from the boiler to where it exits the wall, usually low down near a drain. The blockage is most often at the end or at a bend.
- Check it is safe to reach. Only work at ground level, and watch for ice underfoot.
- Apply gentle warmth. Either hold a hot water bottle or a cloth soaked in warm water against the frozen section, or pour warm water from a jug or watering can slowly along the pipe. Use warm water, never boiling.
- Keep going until it runs. You may hear the boiler gurgle as water drains through.
- Reset the boiler once, following the instructions in your user manual.
If the boiler restarts and runs normally, you are done. Keep an eye on it during the cold spell.
What should you not do?
- Do not use boiling water, a kettle straight off the boil, a heat gun or a naked flame.
- Do not cut or disconnect the pipe.
- Do not remove the boiler casing or the condensate trap.
- Do not keep resetting the boiler if it locks out again.
What if the boiler still will not start?
If the pipe is clear and the boiler still locks out after one reset, the cause may be something else: a blocked condensate trap inside the boiler, an ignition fault or a gas supply problem. See boiler won’t fire up, then send an enquiry with the make, model and fault code. Same-day callouts where available, and frozen pipes are one of the busiest jobs in a Birmingham cold snap.