E127 Boiler Fault Code: What It Means on Every Brand

The E127 fault code appears on 2 brands — Baxi and Navien — 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 2 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 E127 means	Severity	DIY?
BBaxi	The E127 code appears on Baxi boilers when the anti-Legionella protection cycle has failed to reach or maintain its target temperature — typically 60°C or above. Full guide →	Engineer may be needed	No
NNavien	The E127 code on Navien boilers and hot water units indicates a problem with the Air Pressure Sensor (APS) — either an open-circuit or short-circuit fault within the sensor itself. Full guide →	Lockout — engineer likely	No

E127 brand by brand

Baxi E127

The E127 code appears on Baxi boilers when the anti-Legionella protection cycle has failed to reach or maintain its target temperature — typically 60°C or above. Modern Baxi boilers run a periodic programme that heats stored or standing domestic hot water to a high temperature specifically to eliminate any Legionella bacteria that may have developed. When the boiler cannot hit that threshold within the allotted time, it flags E127 as a safety-triggered fault. Because this fault has an indirect public health dimension — Legionella bacteria can cause Legionnaires' disease — it should not be left unresolved or simply reset repeatedly without investigation.

Causes, fixes & costs for Baxi E127 → · All Baxi codes

Navien E127

The E127 code on Navien boilers and hot water units indicates a problem with the Air Pressure Sensor (APS) — either an open-circuit or short-circuit fault within the sensor itself. In practice, particularly on NPN-series units, this code also surfaces when the appliance loses its flame during operation. The two are closely linked: if the combustion fan fails to reach the correct speed, the APS cannot confirm adequate airflow, so the control board aborts the ignition sequence and locks the unit out. The typical homeowner symptom is a complete loss of hot water with the boiler refusing to fire up.

Causes, fixes & costs for Navien E127 → · All Navien codes

Frequently asked questions

Is the E127 fault code the same on every boiler?

No. E127 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 E127 fault myself?

Not usually. On every brand listed, E127 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 E127 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.