Boiler shows F23, heating stops, flow and return temperatures differ greatly

Safety: Isolate power and allow the system to cool before bleeding or opening any components.

Steps:

• Bleed all radiators and the boiler’s air vent to remove trapped air.
• Ensure all radiator and isolation valves are open and that any motorized zone valves are operating correctly.
• Clean system filters and strainers to restore full flow.
• Check the circulation pump speed setting (if adjustable) and increase if necessary within Protherm’s guidelines.
• If the pump is noisy or weak, replace it with the correct Protherm‑approved pump.
• If the system remains imbalanced, a power‑flush may be required to clear sludge from pipework and the primary heat exchanger.

After repair: Reset the boiler and monitor ΔT via diagnostics to ensure it is within acceptable limits and F23 does not recur.