F.23 High
Your boiler has switched itself off because the water temperature inside it is rising much faster than the water temperature being sent to your radiators, usually due to a circulation blockage.
Technical description: Safety switch off temperature difference too great
Typical repair cost: £100-£350 (including labour)
DIY fix possible
Check that all radiator valves (TRVs) are turned to the highest settingEnsure the boiler pressure is between 1.0 and 1.5 bar on the digital displayCheck if any valves underneath the boiler have been accidentally closed
Protect yourself from future repair bills
A boiler cover plan would cover faults like F.23 — no call-out fees, no surprises.
*Affiliate links — we may earn a commission at no extra cost to you. Prices shown are starting prices.
Parts commonly replaced
- Pump
- Flow and Return Thermistors
- Main Heat Exchanger (Cleaning/Descaling)
*Affiliate links — we may earn a commission at no extra cost to you.