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 24 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
- 128 Combi Repair: £90-160
- 615 System 15 Repair: £150-300
- 618 SYSTEM Repair: £150-300
- 624 System 24 Repair: £150-300
- 818 System Repair: £120-200
- 824 SYSTEM Repair: £120-200
- Assure Repair: £150-300
- Duo-tec 2 Combi 28 Compact
- Duo-tec Combi GA Repair: £90-160
- EcoBlue Repair: £120-200
- Ecoblue 12 System ErP Repair: £150-300
- Ecoblue 15 System ErP Repair: £150-300
- Ecoblue 24 System ErP Repair: £150-300
- Ecoblue 28 System ErP Repair: £150-300
- Ecoblue Advance Combi Repair: £120-220
- EcoBlue System Repair: £120-220
- Ecoblue18 System ErP Repair: £150-300
- Neta-tec Combi 24 GA
- Neta-tec Combi 28 GA
- Neta-tec Combi 33 GA
- PLATINUM COMPACT 25 COMBI Repair: £80-£150
- PLATINUM COMPACT 30 COMBI Repair: £80-£150
- PLATINUM COMPACT 36 COMBI Repair: £80-£150
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 31 August 2026