Boiler Pressure Too High in Birmingham

Most combi and system boilers like their pressure at around 1 to 1.5 bar with the heating cold, rising a little as the water warms up. When the needle climbs past 2.5 bar, or into the red zone around 3 bar, something is letting the pressure build, and the boiler will often stop or start dripping water from a pipe outside to protect itself.

The simplest cause is the filling loop. If the system was topped up recently and the valve was left slightly open, or the valve has started to let water through on its own, mains water keeps creeping in and the pressure keeps rising. Check that both taps on the filling loop under the boiler are fully closed.

The next most common cause is the expansion vessel. Water expands as it heats, and the vessel, a small tank with an air cushion inside, absorbs that expansion. Over the years it loses its air charge, so the pressure jumps every time the heating comes on and drops back as it cools. Where that is the fault, the vessel needs re-pressurising or replacing.

When the pressure gets too high, the pressure relief valve opens and lets water out through a copper pipe on the outside wall. That is the safety system working, but once a relief valve has opened a few times it often keeps dripping and needs replacing too. If you see water coming from that pipe, the system needs looking at rather than leaving.

With the heating off and cold, you can let a little pressure out by bleeding a radiator, a towel ready, until the gauge reads about 1.5 bar. If it climbs again, an engineer needs to check the filling loop, the expansion vessel and the relief valve.

A photo of the boiler badge and the display on WhatsApp tells us the make, the model and often the likely part before anyone sets off. If you smell gas, leave the house, do not touch switches and ring the National Gas Emergency line on 0800 111 999 from outside.