Boiler pressure too high: why the gauge keeps creeping up

Things worth knowing about boiler pressure running too high

• Check the filling loop valves are fully closed as the first step
• A loop left slightly open feeds pressure in continuously
• A failed expansion vessel lets heating expansion push pressure too high
• Pressure that rises only while heating is running points to the vessel
• Persistent high pressure risks discharge through the relief valve

Where boiler pressure running too high usually comes from

A filling loop valve left even slightly open is the single most common cause, feeding mains pressure continuously into the sealed system without anyone noticing. A failed expansion vessel that has lost its air charge lets normal heating expansion push pressure far higher than it should. Where pressure only rises while the heating is actively running and falls back once it cools, the vessel is the prime suspect over the filling loop.

Where we deal with this

• Street (BA16) · 14 mi
• Beckington (BA11) · 5 mi
• Wanstrow (BA4) · 9 mi

Questions we get asked

Can I just bleed a radiator to bring pressure down?

That reduces it temporarily but does not fix a stuck filling loop valve or a failed vessel, so it will likely climb again.

Is high pressure as urgent as low pressure?

It should still be checked promptly — sustained high pressure risks the relief valve discharging and wasting water.