E321 High
Your boiler has detected a problem with the sensor that monitors hot water temperature, which may mean you have no hot water or the temperature is inconsistent.
Technical description: Not water thermistor fault
Typical repair cost: £90-160 (including labour)
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Protect yourself from future repair bills
A boiler cover plan would cover faults like E321 — no call-out fees, no surprises.
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Parts commonly replaced
- Hot water NTC thermistor
- Connecting wiring harness
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