Boiler runs but radiators remain cold or only lukewarm

Safety: Radiators and pipes can be hot. Use gloves when bleeding.

• Check valves: Ensure all radiator valves and any isolation valves near the Herz boiler are fully open.
• Bleed radiators: Starting from the lowest floor, bleed each radiator until water flows without air.
• Clean filter: If a Herz dirt separator or magnetic filter is installed, isolate and clean it thoroughly.
• Check pump operation: Feel the flow and return pipes near the boiler. If there is little temperature difference and radiators are cold, the pump may be failing and require replacement.