Radiators Not Heating Up — Troubleshooting and Fixes
Published: July 14, 2026 — CANRO Heating & Cooling — Greater Vancouver, BC
Some Hot, Some Cold
Uneven radiator heating is the most common boiler system complaint in Greater Vancouver. When some radiators heat up normally while others stay cold, the cause is almost always trapped air, system imbalance, sludge buildup, or a failed zone valve.
Step 1: Bleed Air from Radiators
Air rises to the top of radiators. Use a radiator bleed key to open the bleed valve. Hold a cloth to catch water. Turn the key until you hear air hissing. When water flows steadily, close the valve. Check boiler pressure after bleeding — it will drop and may need repressurizing.
Step 2: Balance Your Radiators
The lockshield valve restricts or allows flow. Radiators closest to the boiler get too much flow while distant ones get too little. Open all lockshield valves fully, then gradually close the valves on the hottest radiators by quarter-turns until temperatures even out.
Step 3: Sludge and Zone Valves
If bleeding and balancing do not solve the problem, black magnetite sludge may be blocking flow. A power flush removes sludge and restores flow. A failed zone valve can also cause an entire zone to stay cold. Listen for the valve motor when the thermostat calls for heat — silence indicates a failed actuator.