Boiler shows F.23, intermittent heating, pump noisy or very hot

Safety: Isolate power before opening the boiler. Water may be hot; use caution.

• Check system pressure: Confirm pressure is 1.0–1.5 bar. Low pressure can cause airlocks and poor circulation.
• Bleed pump: Remove the pump bleed screw carefully with a cloth ready. Allow air to escape until water flows steadily, then refit the screw.
• Check pump runs: With the case back on and power restored, call for heat and listen for the pump. If it hums but does not circulate, the impeller may be stuck; a technician can free or replace it.
• Clean filters and strainers: Clean any system filter and the boiler’s internal dirt trap/strainer if fitted.
• Engineer attention: Persistent F.23 after bleeding and cleaning suggests a failing pump or severe system blockage requiring professional flushing or pump replacement.