Why Is My Boiler Losing Pressure? (And When to Call an Engineer)

If your boiler pressure gauge keeps dropping below 1 bar, the most common cause is a small water leak somewhere in your central heating system, though it can also be caused by a faulty pressure relief valve, a failing expansion vessel, or trapped air that's been bled out of a radiator.

How to check: most boilers have a pressure gauge on the front. It should normally sit between 1 and 1.5 bar when the heating is off and cold. If it's regularly dropping below 1, your system needs attention.

Topping up pressure yourself: many combi boilers have a filling loop (a flexible braided hose, usually underneath the boiler) that lets you top up pressure safely by following the instructions in your boiler's manual. If you're not confident doing this, it's completely reasonable to leave it to an engineer.

When it's more than just a top-up job: if you find yourself topping up the pressure every few days or weeks, that's a sign of an underlying leak or fault, not something to keep managing yourself. Left unaddressed, this can cause more expensive damage over time.

Call an engineer if:

• Pressure keeps dropping repeatedly, even after topping up

• You can see visible water anywhere near the boiler, pipework, or radiators

• Your boiler is showing an error code alongside the pressure drop

• You're not comfortable using the filling loop yourself

We cover boiler repairs across Tunbridge Wells, Tonbridge, Cranbrook, Wadhurst, Goudhurst, and Hawkhurst — get in touch if your pressure issue isn't resolving itself.