E21 High
Your boiler has detected that the water returning from your radiators is too hot, causing the system to shut down to prevent damage.
Technical description: Central heating (CH) return sensor overheating
Typical repair cost: £120-250 (including labour)
DIY fix possible
Check that all radiator valves are fully openEnsure the central heating system pressure is between 1.0 and 1.5 barSwitch the boiler off and on again to see if the fault clears after the system cools down
Protect yourself from future repair bills
A boiler cover plan would cover faults like E21 — 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
- CH Return NTC Sensor
- Central Heating Pump
- Secondary Heat Exchanger
*Affiliate links — we may earn a commission at no extra cost to you.