E28 Boiler Fault Code: What It Means on Every Brand

E28 is a flue-thermistor fault on Baxi, Potterton, Main and Andrews (all Baxi-group platforms) — the sensor watching flue-gas temperature has failed or read out of range — while Keston uses E28 for a fan fault. Both are engineer jobs; the flue sensor is inexpensive but sits in the combustion-monitoring chain.

Up to: Lockout — engineer likely 5 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 E28 means	Severity	DIY?
AAndrews	The E28 fault code on Andrews boilers (which share their platform and fault-code conventions with Baxi Group products, including Baxi and Potterton) indicates that the boiler has detected… Full guide →	Lockout — engineer likely	Some checks
BBaxi	The E28 fault code on a Baxi boiler signals a problem detected in the flue circuit — most commonly involving the flue NTC thermistor (the temperature sensor monitoring outgoing flue… Full guide →	Lockout — engineer likely	Some checks
KKeston	The E28 fault code on a Keston boiler indicates that the boiler's fan has failed to operate correctly. Full guide →	Lockout — engineer likely	No
MMain	The E28 fault code on Main boilers indicates a problem with the flue thermistor — a small NTC (Negative Temperature Coefficient) temperature sensor that monitors the temperature of exhaust… Full guide →	Lockout — engineer likely	No
PPotterton	The E28 code on a Potterton boiler indicates a fault with the flue thermistor — the sensor responsible for monitoring the temperature of exhaust gases leaving the boiler. Full guide →	Engineer may be needed	No

E28 brand by brand

Andrews E28

The E28 fault code on Andrews boilers (which share their platform and fault-code conventions with Baxi Group products, including Baxi and Potterton) indicates that the boiler has detected a problem related to the flue thermistor (NTC sensor) or has registered an issue consistent with a blocked or obstructed flue, or a frozen condensate pipe. In either scenario the boiler locks out as a safety precaution and will not restart until the root cause is resolved and the fault is cleared. The flue NTC is a small temperature-sensing probe that monitors exhaust gas temperatures in the flue; if it reads outside expected parameters — whether through sensor failure, wiring loss, or actual abnormal flue conditions — the boiler registers E28 and shuts down. Note: Andrews Water Heaters is part of the Baxi Group; always cross-reference with your specific Andrews model manual or contact Andrews Technical Support to confirm applicability to your exact unit.

Causes, fixes & costs for Andrews E28 → · All Andrews codes

Baxi E28

The E28 fault code on a Baxi boiler signals a problem detected in the flue circuit — most commonly involving the flue NTC thermistor (the temperature sensor monitoring outgoing flue gases), the air pressure switch, or a physical blockage in the flue or condensate drain. When this fault triggers, the boiler locks out as a safety precaution and will not fire until the underlying issue is identified and resolved. The flue thermistor sits in the flue gas outlet and continuously feeds temperature data back to the PCB; if those readings fall outside expected parameters — or if flue gas flow is impeded — the boiler shuts down rather than risk an unsafe condition.

Causes, fixes & costs for Baxi E28 → · All Baxi codes

Keston E28

The E28 fault code on a Keston boiler indicates that the boiler's fan has failed to operate correctly. When the boiler calls for heat, it expects the fan to reach its target speed within a few seconds. If that doesn't happen — or if the control board doesn't receive the expected signal back from the fan — the boiler locks out and displays E28. The fan is a safety-critical component: its job is to push combustion gases safely out through the flue. Without a confirmed working fan, the PCB refuses to open the gas valve, so no heat or hot water is produced until the underlying fault is resolved and the boiler is manually reset.

Causes, fixes & costs for Keston E28 → · All Keston codes

Main E28

The E28 fault code on Main boilers indicates a problem with the flue thermistor — a small NTC (Negative Temperature Coefficient) temperature sensor that monitors the temperature of exhaust gases leaving the boiler through the flue. When this sensor sends a reading outside the expected range, or stops communicating with the control board altogether, the boiler locks out as a safety measure. The fault can also be triggered by a blocked or frozen condensate pipe, a flue obstruction restricting gas flow, wiring faults between the sensor and the PCB, or — less commonly — a failing gas valve or PCB itself. Because Main boilers share their fault code architecture with Baxi and Potterton (all part of the BDR Thermea Group), the E28 code carries the same meaning across all three brands.

Causes, fixes & costs for Main E28 → · All Main codes

Potterton E28

The E28 code on a Potterton boiler indicates a fault with the flue thermistor — the sensor responsible for monitoring the temperature of exhaust gases leaving the boiler. When this sensor stops working correctly, the boiler's control board can no longer confirm that combustion gases are being expelled safely, so it shuts down as a precaution. You may notice the boiler firing up and beginning to warm the system before cutting out before radiators reach temperature. The E28 appears across a number of Potterton models including the Combi Gold HE A, Combi Promax HE Plus, and Promax System HE Plus. Because the flue system is directly linked to safe boiler operation, this fault should be investigated promptly rather than repeatedly reset and ignored.

Causes, fixes & costs for Potterton E28 → · All Potterton codes

Frequently asked questions

Is the E28 fault code the same on every boiler?

No. E28 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 E28 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. The underlying repair usually needs a registered engineer. Never open the boiler casing yourself.

Who should I call about a E28 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.