Boiler runs but radiators remain cold or only lukewarm

Safety: Allow system to cool before working on valves or bleeding radiators.

• Check boiler flow/return temperatures: If the boiler is hot but radiators are cold, circulation is restricted.
• Bleed radiators: Starting from the top floor, bleed air until water flows steadily.
• Check zone valves: Ensure motorised valves (if fitted) are in the open position when heating is demanded. Some have a manual lever you can move to open.
• Inspect system filter: If a magnetic filter is installed, have it cleaned by a competent person.
• Call a technician: They can test and replace the circulation pump, flush the system, and verify correct valve operation.