Boiler Pressure Guide

Most combi boilers operate between 1 and 1.5 bar when the system is cold. Pressure can rise slightly when the system heats up — this is normal and usually stays below 2 bar.

Check the pressure gauge on the front of your boiler or on the filling loop assembly. If you are unsure what range is correct for your model, the user manual or manufacturer label will confirm the ideal cold pressure.

Persistent low pressure often indicates a leak on the heating system, a failing expansion vessel or a recently bled radiator without repressurising. A one-off drop after bleeding is normal — top up using the filling loop following manufacturer instructions.

If pressure drops again within days, do not keep topping up indefinitely. A hidden leak or component failure needs professional diagnosis. APS engineers trace pressure loss across radiators, pipework and the boiler itself.

Pressure that keeps rising above 2.5 bar may indicate a faulty expansion vessel, a filling loop left open or a problem with the pressure relief valve. Excessive pressure can cause leaks at radiator valves and damage components.

If the pressure relief valve discharges water outside, switch off the boiler and call a qualified engineer. Do not attempt to disable safety devices.

Call 01635 269888 if repressurising does not hold, the boiler locks out with a pressure fault code, or you see water leaking from the boiler or pipework. Our Gas Safe engineers serve Newbury, Thatcham and Berkshire daily.