Boiler Pressure & Leaks FAQs
Practical answers from our Gas Safe engineers on the most common pressure and leak issues — simple checks you can do before calling us out.
Why does my boiler keep losing pressure?
Most boilers lose pressure when there’s a small leak in the system or trapped air in the radiators. Try bleeding your radiators and then repressurising using the filling loop to 1–1.5 bar. If pressure keeps dropping, a leak needs attention.
How do I repressurise my boiler safely?
Turn off the boiler, attach the filling loop and slowly open both valves until the pressure gauge reaches 1–1.5 bar, then close them. Switch the boiler back on and check for leaks or drips around the system.
Can a small leak cause my boiler to shut down?
Yes. Even a slow drip can reduce pressure below the safety threshold and trigger a lockout. It’s designed to protect the system — call a qualified engineer if it keeps happening.
Is it normal for pressure to rise when the heating is on?
A slight rise (up to about 2 bar) is normal as water expands with heat. If it climbs much higher, the expansion vessel or pressure relief valve might need checking.
How can I spot hidden leaks?
Look for damp patches near radiators, ceilings below pipe runs, or under the boiler itself. Sometimes leaks are behind walls or under floors — engineers can trace them using leak-detection fluid or thermal imaging.