Boiler losing pressure repeatedly (Worcester Bosch, Ideal & Vaillant)
⚠️ This needs a qualified professional
This fault involves gas or mains electrical work. Don't attempt a DIY repair — UK law requires gas work to be carried out by a Gas Safe registered engineer. Below is what to check and describe to them, not step-by-step repair instructions.
Modern combi boilers should sit at around 1–1.5 bar on the pressure gauge when cold. If you find yourself repressurising (topping up via the filling loop) every few days or weeks, there’s a leak somewhere in the system — it just isn’t always visible.
What’s safe to check yourself
- Look for damp patches, staining, or drips around visible pipework, radiator valves, and under the boiler itself.
- Check radiators for weeping from the bleed valve or the valve connections at each end.
- Note how often you’re having to top up — “once a week” vs “twice a day” is useful information for the engineer and points to how urgent the leak is.
- Check the pressure relief valve (usually a small pipe that exits outside the house, often near the boiler) for drips — a dripping external pipe is a strong sign of a fault, worth mentioning when you call.
Don’t attempt to fix a pressure loss issue yourself. Repressurising via the filling loop occasionally is fine (check your manual for the exact steps for your model), but tracing and fixing an actual leak, or working inside the boiler casing, is gas and heating engineer work. If your boiler is losing pressure quickly (same day) or you smell gas, turn it off, don’t attempt any repair, and call a Gas Safe registered engineer — or the National Gas Emergency Service on 0800 111 999 if you suspect a gas leak specifically.
What to tell the engineer
How often you’re topping up, whether you’ve found any visible damp/dripping, and whether the boiler shows any fault code on its display when it happens — this saves them a diagnostic step.