Combi Boiler Water Pressure Issues — Complete Troubleshooting
Published: July 23, 2026 — BC Wide Home Services Ltd, doing business as BC Wide Heating & Air Conditioning — Greater Vancouver, BC
Low Pressure (Below 1 Bar)
If the boiler pressure gauge reads below 1 bar, the system needs more water. Use the filling loop (flexible braided hose) to repressurize — open both valves slowly until the gauge reads 1.0-1.5 bar, then close both valves tightly. If pressure drops again within days, there is a leak in the system that needs professional investigation.
High Pressure (Above 2.5 Bar)
If the pressure gauge reads above 2.5 bar when the boiler is cold, the expansion tank may have failed, or the filling loop was left open. Check that the filling loop valves are fully closed (both handles perpendicular to the pipe). If closed and pressure is still high, the expansion tank needs professional service. Bleed a small amount of water from a radiator to reduce pressure temporarily.
Normal Pressure Range
Normal boiler pressure: 1.0-1.5 bar when cold. When the boiler runs, pressure may rise to 1.5-2.5 bar — this is normal (water expands when heated). If pressure exceeds 3 bar, the pressure relief valve will discharge water. Regularly check the pressure gauge — pressure that fluctuates wildly indicates a problem.