Boiler runs but some or all radiators/baseboards stay cold

Safety first: Turn off power before working on pumps or valves. Hot water can cause burns.

• Feel supply and return pipes: When the boiler is firing, the main supply should be hot. Compare each zone's supply and return; a cold return may indicate no flow.
• Check circulator operation: For each zone pump, feel for vibration and warmth when that zone calls. If a pump is cold and silent, check its power and relay.
• Inspect zone valves: For motorized valves, verify the manual lever moves freely and the valve opens when the thermostat calls.
• Bleed air: Use purge valves or radiator bleeders on the affected zone to remove trapped air until water flows steadily.
• Adjust balancing valves: Ensure any manual balancing valves are open enough to allow flow.