If your boiler keeps losing pressure, you are not alone — it is one of the most common heating problems we are called out to across Surrey and Sussex. The good news is that it is often something you can check yourself, and even the fixes that need a plumber are usually straightforward.
What boiler pressure should be
Look at the pressure gauge on the front of your boiler. When the heating is off and the system is cold, it should sit at roughly 1.0 to 1.5 bar. If the needle is below 1 bar — often in the red zone — your boiler has lost pressure and may shut down or fail to heat properly.
The most common cause: a leak
A system that slowly loses pressure over days or weeks almost always has a small leak somewhere. Check around radiator valves, visible pipework, and under the boiler for damp patches, drips, or tell-tale limescale staining. Never ignore water near electrics — switch off and call us if you find it around the boiler itself.
Recently bled your radiators?
Bleeding radiators releases trapped air but also lets pressure out of the system. If your pressure dropped straight after bleeding, that is normal — you simply need to top it back up.
A faulty valve or expansion vessel
If pressure climbs too high when the heating is on and then drops when it cools, the expansion vessel or pressure relief valve may be failing. These are internal boiler parts and should be checked by a qualified engineer — not a DIY fix.
How to re-pressurise your boiler
Most boilers have a filling loop — a silver braided hose with a valve at each end underneath. With the boiler off and cold, open both valves slowly, watch the gauge rise to around 1.2 bar, then close both valves firmly and turn the boiler back on. If you are unsure where your filling loop is, check the manual or call us before touching anything.
When to call a plumber
If the pressure keeps dropping after you top it up, you cannot find the leak, or the boiler is showing a fault code, get it looked at. We cover Crawley, Horsham, Brighton and the surrounding areas — call 07719 522450 or WhatsApp us.