E50 Boiler Fault Code: What It Means on Every Brand

The E50 fault code appears on 3 brands — Baxi, Main and Potterton — and it does not mean the same thing on each. The same two or three characters can signal a pressure problem on one boiler and an ignition fault on another, so identify your brand first and use the table below to jump to the right page.

Up to: Lockout — engineer likely 3 brands use this code Meaning differs by brand

Which brand is your boiler?

The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.

Brand	What E50 means	Severity	DIY?
BBaxi	The E50 fault code on Baxi boilers indicates a problem with the domestic hot water (DHW) NTC (Negative Temperature Coefficient) temperature sensor. Full guide →	Lockout — engineer likely	No
MMain	The E50 code appears on your Main boiler display (shown as 'E' followed by '50') when the control board detects a problem with the Domestic Hot Water (DHW) NTC thermistor sensor — the… Full guide →	Lockout — engineer likely	No
PPotterton	The E50 code on a Potterton boiler points to a problem with the domestic hot water (DHW) NTC thermistor — the temperature sensor that monitors the heat of your hot water supply. Full guide →	Engineer may be needed	No

E50 brand by brand

Baxi E50

The E50 fault code on Baxi boilers indicates a problem with the domestic hot water (DHW) NTC (Negative Temperature Coefficient) temperature sensor. The boiler's control board continuously monitors resistance readings from this thermistor to track how hot the water is — when that resistance falls outside the expected range, the board concludes the sensor is unreliable and locks the boiler out as a safety precaution. On certain models such as the Baxi Platinum, E50 can also be triggered when the maximum permissible flow temperature is exceeded and the PCB steps in to halt operation. In either case, the boiler will not fire until the fault is diagnosed and cleared.

Causes, fixes & costs for Baxi E50 → · All Baxi codes

Main E50

The E50 code appears on your Main boiler display (shown as 'E' followed by '50') when the control board detects a problem with the Domestic Hot Water (DHW) NTC thermistor sensor — the component responsible for measuring the temperature of your hot water. The board continuously monitors the electrical resistance of this sensor, which rises and falls in a predictable pattern as water temperature changes. When that resistance reading falls outside the acceptable range — either because the sensor circuit has broken open (open circuit) or has shorted internally (short circuit) — the boiler locks out and displays E50 as a safety precaution. Because Main boilers share the same platform and PCB architecture as Baxi and Potterton models (all sit under the Baxi Heating UK group), this fault code carries identical meaning across all three brands. The boiler will not resume normal operation until the underlying sensor fault is resolved and the error is cleared.

Causes, fixes & costs for Main E50 → · All Main codes

Potterton E50

The E50 code on a Potterton boiler points to a problem with the domestic hot water (DHW) NTC thermistor — the temperature sensor that monitors the heat of your hot water supply. Think of it as the boiler's thermometer for the hot water circuit: it sends resistance readings to the control board that change in proportion to the water temperature. When those readings drift outside the acceptable range — whether because the sensor has failed, its wiring is compromised, or water circulation isn't delivering heat properly — the control board logs E50 and typically suspends the hot water function as a precaution. Central heating may continue to work normally, but taps will run cold until the fault is resolved.

Causes, fixes & costs for Potterton E50 → · All Potterton codes

Frequently asked questions

Is the E50 fault code the same on every boiler?

No. E50 means different things on different brands — see the table above. Always identify your boiler's brand (it is printed on the front casing) before acting on any advice about the code.

Can I fix a E50 fault myself?

Not usually. On every brand listed, E50 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.

Who should I call about a E50 fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.

General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.