1. Look for an outdoor pipe
(usually white plastic similar to a waste pipe) which is connected to your boiler.
2. Pour warm water (not boiling)
If it’s safe and easy to get to, and access is available at ground level, pour warm water (not boiling) along the length of the pipe. Or put a hot water bottle or heat pad on the sections of pipe you think are frozen.
3. Reset your boiler.
If the pipe has defrosted, your boiler should start as normal.