Boiler pressure: how to check it and what to do if it drops

Why pressure matters

A closed heating circuit works with enough water pressure for water to circulate everywhere and for the appliance to stay protected. Too low and the boiler may lock out; too high and the relief valve may open. The correct range is in your model’s manual and on the gauge.

Where to read the pressure

Most boilers have a gauge or show the value on the screen. Read it cold if you can. If the reading varies a lot between heating off and running, note both values: it is useful information for the engineer.

If the pressure is too low

First look for a visible leak (radiators, joints, the floor under the appliance). If your model’s manual allows it, you can slowly top up the water with the filling loop to the indicated range. Do not do it several times a week: pressure that keeps dropping reveals a leak that needs tracing.

If the pressure is too high

Switch the heating off and let the circuit cool before reading the value again. Do not open the safety valve to “drain” the circuit. Pressure that rises again after cooling can point to a worn expansion vessel or overfilling.

Frequently asked questions

The right next step

Observe the symptoms, avoid risky handling and note what changes. For a recurring problem or a renovation project, an on-site diagnosis lets you choose a suitable solution rather than a temporary fix.