Boiler Losing Pressure: Causes and What to Do

Normal pressure in a domestic gas boiler is 1.2–1.5 bar when cold. If the gauge needle falls below 1 bar, the boiler shows an error and shuts off the heating. Here's why it happens and what to do.

Important: if you need to top up more than once a month — there is a leak in the system, and it won't fix itself. The longer you wait, the more expensive the repair.

Why pressure drops

A leak in the system — the most common cause. Check pipe joints, radiators and the floor under the boiler for wet spots, drips or rusty marks.
You bled the radiators — water leaves with the air, so pressure drops. That's normal: just top the system up.
Expansion vessel — if pressure jumps up when heating and falls when cooling, the vessel's membrane has likely failed.
Safety valve — if the discharge pipe drips, the valve doesn't hold. It needs replacing.
Heat exchanger micro-crack — water escapes inside the boiler. The sign: pressure drops but no visible leak anywhere.

How to raise the pressure yourself

Find the filling valve

Usually under the boiler — a tap or lever on the cold water pipe

Open it slowly

Watch the pressure gauge needle start to rise

Stop at 1.2–1.5 bar

Never above 2 bar! Close the valve

Restart the boiler

The pressure error should clear

When to call a technician

If pressure drops again within a day or two after topping up, jumps while heating, or the discharge pipe drips — you need diagnostics. We find the cause in one visit: diagnostics 50 ₾, free with repair.

Pressure keeps dropping?

We'll find the leak and fix the cause. 6-month warranty.

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Boiler Losing Pressure — What to Do