Frozen Condensate Pipe — Thaw & Prevent (UK 2026)
Every UK cold snap generates a wave of combi boiler lockouts — usually the frozen condensate pipe. Here is how Gas Safe engineers thaw it in 15 minutes.
Step-by-step method
1. Confirm the fault
Look for EA (Worcester), F28 (Vaillant), F1 gurgling (Ideal). Then trace the small plastic pipe (usually 22mm white) from the base of the boiler to outside.
2. Pour warm (not boiling) water
Kettle boiled + cooled 5 min = ~60°C. Pour along the exposed pipe. Boiling water can crack plastic.
3. Focus on the U-bend outside
90% of freezes happen at the external bend or exit fitting. Wrap a warm cloth around it if you can't pour.
4. Reset the boiler
Hold reset for 3 seconds. Should refire immediately.
5. Prevent recurrence
Lag the entire external pipe with 25mm Armaflex. Consider reducing exposed length by re-routing to a soil stack inside.
Frequently asked questions
Can I use boiling water on the pipe?+
No — plastic condensate pipe can craze and crack. Use warm water (below 70°C) or a warm cloth.
Why does my condensate pipe keep freezing?+
Undersized (should be 32mm+ external), too much length outside, no lagging, or discharge into open air rather than a drain.