Why is my boiler losing pressure?

What counts as normal pressure

Most household combi boilers read somewhere between 1 and 1.5 bar when the system is cold, and climb to about 2 bar once it's up to temperature. Drop under roughly 0.7 bar and most boilers will lock themselves out as a safety measure, rather than keep running.

The three most common culprits

Nine times out of ten, falling pressure comes down to one of these:

• A small leak somewhere in the pipework, at a radiator valve, or around a towel rail. Check for damp patches, rust staining, or marks on floorboards and ceilings below pipe runs.
• An expansion vessel that's lost its charge and can no longer take up the extra volume as water heats up. A tell-tale sign is pressure that shoots up when the heating's on, then falls well below normal once everything cools.
• A pressure relief valve that's weeping, usually seen as an occasional drip from the small copper pipe that discharges outside the property.

Topping the pressure back up

With the boiler switched off and cold, you can normally re-pressurise using the filling loop underneath it: open both valves gradually until the gauge shows around 1.2 bar, then shut them off firmly. Never leave the filling loop open, and don't get into a habit of topping up week after week, that's usually a leak being disguised rather than fixed, and repeatedly adding fresh water pushes oxygen into the system, which corrodes radiators from within over time.

When it's time to bring in a Gas Safe engineer

Topping up more than once or twice a year is a sign to get it looked at properly. Pressure testing, recharging the expansion vessel, and tracing a leak all mean draining the system down, which is engineer's work. If you'd rather hand it to someone qualified, we work right across Halesowen, Stourbridge, Dudley and the wider West Midlands, and we book urgent repairs in fast, usually next day.