Boiler runs but radiators stay cold or only lukewarm

Safety first: Allow radiators to cool slightly before bleeding to avoid scalding.

• Check thermostat and timers: Ensure room thermostats are calling for heat and programmer is set to heating ON.
• Bleed radiators: Starting with the highest floor, bleed each radiator until water flows steadily. Re-pressurise the system as needed.
• Feel flow and return pipes: At the boiler, the flow should be hot and the return warm. If both are only slightly warm, the pump may not be circulating properly.
• Check zone valves: If fitted, ensure motorised valves are opening (lever moves freely when calling for heat).
• Professional powerflush: If some radiators remain cold or have cold spots, a Nibe technician may recommend a system powerflush and pump replacement.