BoilerTroubleshooting2026-02-26
Boiler Pressure Too High: Causes and Fixes
High boiler pressure usually means over-filling or a faulty filling loop — here's how to lower it safely.
If your boiler pressure reads above about 2.5 bar, it's too high and can trip the relief valve. Here's why and what to do.
Why pressure climbs
Over-filling via the filling loop, a filling loop left slightly open, or a faulty pressure gauge are common causes; a failing expansion vessel makes pressure swing high when hot.
How to lower it
Bleeding a radiator releases a little water and pressure; if it keeps climbing, the expansion vessel or filling loop needs a technician.
Key takeaways
- Normal cold pressure is 1–1.5 bar
- Check the filling loop is fully closed
- Bleed a radiator to release excess
- Persistent high pressure needs service
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