Boiler pressure too high — over 3 bar
Check the steps below first — if you\'re not confident, get it fixed safely today.
Find a Gas Safe engineer near you →⚠️ Do not operate the boiler if the pressure is above 3 bar. Overpressure can cause the pressure relief valve to discharge scalding hot water. If the pressure relief valve is continuously discharging, call a Gas Safe engineer immediately.
Not sure if this matches your problem?
Use our interactive tool — answer a few questions and get a personalised diagnosis.
Most likely cause & what to check
Switch the boiler off and allow the system to cool for 30 minutes. Pressure will often drop slightly as the system cools.
Locate the pressure relief valve (PRV) — a brass valve with a pipe leading outside the property (the discharge pipe). If it is dripping, pressure has already been relieved — this is normal behaviour of a safety device, but indicates the system is overpressured.
Check that the filling loop (the braided hose connecting two valves beneath the boiler) is not left open — this is the most common cause of overpressure. Both valves on the filling loop should be closed when not in use.
If the system is overpressured and the filling loop is already closed, you can bleed several radiators simultaneously to release some system water and bring pressure down to 1–1.5 bar.
If pressure continues to rise after the system heats up, the expansion vessel has failed — this requires a Gas Safe engineer to replace it.
Not confident doing this yourself?
Post the job and we'll match you with vetted local engineers. Free, no obligation.
🛠 Tools & materials you may need
Find a Gas Safe registered engineer near you and get it fixed properly.
Was this guide helpful?