BoilerFaultCodesBaxi 321 Fault Code
The Baxi 321 fault code means: your boiler is struggling to accurately measure the temperature of your hot water, which usually means the water will either be too cold or not come on at all.. It appears on 13 Baxi models in our database.
Technical description: Hot Water NTC Fault
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Baxi models that show the 321 fault code
Click a model for the full fault code list and model-specific repair notes.
- 124 Combi Repair: £90-160
- 200 / 400 Combi Repair: £120-220
- 600 Combi (range) Repair: £90-160
- 624 Combi Repair: £90-160
- Assure Repair: £150-300
- Duo-tec Combi GA Repair: £90-160
- Duo-tec Combi HE A Repair: £120-220
- EcoBlue Repair: £120-200
- Ecoblue Advance Combi Repair: £120-200
- EcoBlue Advance Heat Repair: £90-160
- EcoBlue Heat Repair: £90-160
- EcoBlue Plus Combi Repair: £90-160
- EcoBlue System Repair: £120-220
Source
Baxi 321 fault code information on this page is sourced and cross-checked against the official Baxi service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026