Boiler Pressure Relief Valve Discharging Water — What to Do
Published: July 23, 2026 — BC Wide Home Services Ltd, doing business as BC Wide Heating & Air Conditioning — Greater Vancouver, BC
Why the PRV Discharges
The pressure relief valve discharges water when system pressure exceeds 3 bar (30 PSI). Common causes: expansion tank has failed (can no longer absorb pressure), the boiler is overheating and pressure is rising due to thermal expansion, the filling loop was left open (constantly adding water), or the PRV itself has failed and needs replacement.
What to Do
If water is discharging from the PRV pipe: check the system pressure gauge — if it is reading above 2.5 bar, turn off the boiler and let it cool. If the pressure drops after cooling, the expansion tank likely needs service. If pressure remains high even when cold, the PRV may be faulty. Place a bucket to catch the water and call for professional service.
When It Is an Emergency
If the PRV is discharging continuously and cannot be stopped, turn off the boiler and shut off the water supply to the system. Continuous discharge can flood your mechanical room and damage the boiler control board. Call for emergency service. Do not try to cap or block the PRV discharge pipe — the valve is a critical safety device.