Verified boiler fault code
Potterton E321 Fault Code (Assure Combi & System)
Domestic-hot-water NTC sensor fault, short circuit or open circuit.
Safety disclaimer
Fault code summary
- Manufacturer
- Potterton
- Fault code
- E321
- Fault type
- Temperature sensor, Hot water
- Severity
- Not specified
- Reset
- Not specified
- Applicable models
- Potterton Assure Combi, Potterton Assure System
Quick answer
Domestic-hot-water NTC sensor fault, short circuit or open circuit.
What does this fault code mean?
Domestic-hot-water NTC sensor fault, short circuit or open circuit.
Common causes
- DHW NTC sensor short circuit or open circuit.
Symptoms
- The boiler displays E321 and hot-water operation may stop.
What can the homeowner safely check?
- Note the code and consult the Potterton instructions.
Boiler reset information
Reset information was not provided in the verified manufacturer source. Do not repeatedly reset an unresolved fault.
When should I call an engineer?
Contact a suitably qualified heating engineer when the fault persists, the boiler locks out, or the manufacturer instructions do not resolve it. For gas appliance work in the UK, use a Gas Safe registered engineer.
Engineer diagnosis
- Test the DHW NTC sensor and associated wiring.
Applicable boiler models
Related fault codes
- E09 — Assure Combi & System
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Precirculation alarm.
Read fault code - E110 — Assure Combi & System
The boiler maximum temperature was exceeded, or the safety thermostat sensor tripped.
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Water pressure is low, below 0.5 bar.
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Differential water-flow switch fault; the switch is still open.
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Water circulation fault.
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Safety error for frequent loss of flame.
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Manufacturer documentation
Boiler Error Codes | BaxiPotterton Assure Combi & System — E321 / 163: Domestic Hot Water NTC sensor fault (s.c. or o.c.).
Last verified
2026-09-12
Frequently asked questions
What does Potterton E321 mean?
Domestic-hot-water NTC sensor fault, short circuit or open circuit.