Boiler runs but radiators do not get hot or only partially warm up.

Safety: Allow radiators to cool slightly before bleeding to avoid scalds.

• Bleed radiators: Starting from the highest floor, bleed each radiator until water flows steadily. Recheck boiler pressure and top up if needed.
• Check valves: Ensure all radiator valves and any isolation valves near the Defro boiler are fully open.
• Adjust pump speed: If the Defro pump has multiple speed settings, increase to a higher setting to improve circulation.
• System cleaning: If some radiators remain cold at the bottom, the system may need powerflushing or chemical cleaning by a professional.