Boiler losing pressure? What to check before you call a plumber

A boiler that keeps losing pressure is one of the most common call-outs we get in Bristol. Often it is something you can sort in five minutes. Sometimes it is not. Here is how to tell the difference.

Check the pressure gauge first

Most combi boilers want to sit between 1 and 1.5 bar when cold. If the needle is below 1, the boiler will often shut itself down rather than run dry. That is the boiler protecting itself, not a fault.

Top it up using the filling loop

Under the boiler you will find a braided silver hose with a valve at each end. Open both slowly, watch the gauge climb to about 1.2 bar, then close them again. If the pressure holds for a week, you had a slow drop and nothing more.

When it keeps dropping

If you are topping up more than once a month, something is letting water out. The usual culprits are a leaking radiator valve, a failed expansion vessel, or a pressure relief valve weeping outside. The last two need an engineer.

When to stop and call someone

Call a Gas Safe registered engineer if you can smell gas, if there is visible water around the boiler, if the pressure drops to zero within a day, or if the boiler locks out with a fault code after refilling. Those are not DIY jobs.

We cover Bristol and the surrounding areas for boiler repairs, and we are Gas Safe registered.

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