Why does my boiler keep losing pressure?
What the pressure gauge means, how to top it up, and when it's time to call a plumber.
Most combi boilers like to sit at about 1 to 1.5 bar when the heating is off. If the needle keeps dropping below 1, the boiler may stop working.
Topping it up
Your boiler manual will show you the filling loop, usually a small tap or two under the boiler. Open it slowly until the gauge reads about 1.2 bar, then close it. If you’re not sure, call us.
Why it keeps dropping
If you have to top it up more than once every few months, water is escaping somewhere. Common causes:
- A small leak on a radiator valve or a pipe joint (look for staining or green crust).
- The pressure relief valve letting water out through the pipe outside.
- Bleeding radiators recently, which lets out water as well as air.
A leak won’t fix itself, so it’s worth getting it looked at before it gets worse.