Flow/return temperature difference too high, boiler shuts down to protect heat exchanger

Safety: Allow the system to cool before working on pipework or filters.

• Check all valves: Confirm that all flow and return valves at the boiler and on the system are fully open.
• Clean system filter: If a magnetic or Y-strainer filter is installed, isolate it, remove the cap, and clean out sludge and debris.
• Verify pump speed: On pumps with adjustable speed, ensure the setting is appropriate for the system. Increase speed if necessary.
• Bleed pump and radiators: Bleed air from the pump vent screw (if present) and from radiators.
• Persistent F23: If the fault continues, a technician should check pump performance and inspect the heat exchanger for blockage.