Boiler Pressure Too High — What to Do

High Boiler Pressure — Causes and Fix

Normal boiler pressure is 1–1.5 bar when cold, rising to 2 bar when hot. Above 2.5 bar is considered high; above 3 bar, the pressure relief valve will release water.

What Causes High Pressure?

• The filling loop has been left open accidentally
• The filling loop valve is faulty and allowing water in continuously
• Expansion vessel failure (vessel can't absorb pressure changes)

How to Reduce Pressure Safely

1. Turn off the heating and let it cool
2. Check the filling loop — ensure both valves are fully closed
3. Bleed a radiator — this releases a small amount of water and reduces pressure
4. Monitor the pressure — if it drops to normal (1–1.5 bar) and stays there, problem solved
5. If pressure keeps rising, the expansion vessel may have failed. Call an engineer.