Potterton E20 fault code: what it means and what to do

On a Potterton Assure combi or system boiler, fault code E20 means the boiler has detected a problem with the central-heating NTC temperature-sensor circuit. The manufacturer lists it as a short circuit or open circuit.

Potterton fault meanings are model-specific. Confirm the full model before relying on this explanation; an E20 displayed on a different Potterton range may not have the same meaning.

What does the central-heating NTC sensor do?

The sensor measures the temperature of water in the heating circuit. The boiler uses that reading to control heat output and operate within safe temperature limits.

If the sensor circuit is open or shorted, the control system cannot trust the reading. The boiler may stop heating and display E20 rather than continue with unreliable temperature information.

What can cause Potterton code E20?

The cause may be the temperature sensor, its connector, wiring or the boiler control electronics. The code identifies the affected circuit but does not prove which part has failed.

These components are inside the appliance. Do not remove the casing, unplug leads, test electrical resistance, bridge connections or try to replace the sensor yourself. Internal gas-boiler work should be carried out by a suitably qualified Gas Safe registered engineer.

What can you check safely?

Check that the boiler has electrical power and that your room thermostat, timer or programmer is set normally. If the code appeared after a power interruption or previous intermittent heating, make a note for the engineer.

Keep the casing closed. Turning the room thermostat higher will not repair a faulty sensor circuit, and topping up system pressure will not directly correct E20 unless a separate pressure fault is also present.

Can I reset a Potterton E20 fault?

Use only the reset method in the user guide for your exact boiler. If that guide allows a homeowner reset, try it once.

If E20 remains, returns or the boiler repeatedly locks out, stop resetting it and arrange a repair. A recurring temperature-sensor circuit fault needs proper testing.

Will E20 stop heating and hot water?

Central heating is likely to be affected because the boiler cannot rely on its heating-water temperature reading. Depending on the exact appliance and fault state, hot water may also be unavailable. If the boiler temporarily starts again but E20 returns, the underlying issue still needs attention.

What will an engineer do?

The engineer will confirm the model, inspect the stored fault information and follow the correct Potterton/Baxi service procedure. They may test the sensor, connectors, wiring and control electronics. The repair should follow the test results rather than replacing parts solely because E20 is displayed.

Quick answer

On Potterton Assure boilers, E20 means a central-heating NTC sensor open-circuit or short-circuit fault. Keep the casing closed, use one model-approved reset at most, and book a repair if the code remains or returns.