How to Remove Air from Your Boiler Heating System

Published: July 21, 2026 — CANRO Heating & Cooling — Greater Vancouver, BC

Bleeding Radiators

Start with the lowest radiator and work upward. Use a radiator key to open the bleed valve slightly — you will hear air hissing out. When water trickles out steadily, close the valve. Check boiler pressure after bleeding — it will drop and may need repressurizing to 1-1.5 bar.

Automatic Air Vents

Modern boiler systems have automatic air vents (AAVs) that self-bleed trapped air. If they fail or become blocked, air accumulates in the system. Clean or replace AAVs annually. Manual vents are also available that require periodic operator bleeding.

Persistent Air Problems

If air returns to the system days after bleeding, there is likely a system leak drawing in air, or the expansion tank has failed and is causing cavitation. A leak detection inspection and expansion tank pressure check are needed.

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Safety Reminder

If you smell gas, suspect carbon monoxide or believe there is an immediate danger, leave the property and contact emergency services or the appropriate gas emergency authority. Do not remain inside — exit the building immediately and call for help from outside.