BoilerFaultCodesPotterton E321 Fault Code
The Potterton E321 fault code means: your boiler's temperature sensor for hot water has stopped communicating correctly, which means you may have inconsistent or no hot water at your taps.. It appears on 2 Potterton models in our database.
Technical description: Hot water thermistor fault
What causes the Potterton E321 fault?
This fault occurs when the temperature sensor responsible for your hot water fails to send a clear signal to the boiler's main control board. The most common reason is that the sensor has physically degraded over time or developed an electrical short, meaning the boiler can no longer tell how hot the water is. On some occasions, the issue may also be caused by loose or damaged wiring connecting the sensor to the rest of the system.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Potterton models that show the E321 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton E321 fault code information on this page is sourced and cross-checked against the official Potterton service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026