E164 Boiler Fault Code: What It Means on Every Brand

The E164 fault code appears on 3 brands — Baxi, Biasi 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 E164 means	Severity	DIY?
BBaxi	The E164 fault code on a Baxi boiler signals that the boiler's control system has detected an open or absent signal from the hydraulic differential pressure switch (also referred to as the… Full guide →	Lockout — engineer likely	Some checks
BBiasi	The E164 fault code on Biasi boilers — sometimes shown as A07 on certain models — indicates a problem with the domestic hot water (DHW) temperature sensor. Full guide →	Lockout — engineer likely	No
PPotterton	The E164 code appears on Potterton boilers when the control board detects a problem with the domestic hot water (DHW) NTC (negative temperature coefficient) thermistor — the sensor… Full guide →	Engineer may be needed	No

E164 brand by brand

Baxi E164

The E164 fault code on a Baxi boiler signals that the boiler's control system has detected an open or absent signal from the hydraulic differential pressure switch (also referred to as the flow switch). In plain terms, the boiler expects confirmation that water is circulating at the correct pressure and flow before it will fire, and that confirmation signal is missing. As a safety measure, the boiler locks out completely and will not restart until the underlying problem is resolved. The issue can stem from genuinely low water pressure, a faulty or disconnected switch, wiring problems, or — less commonly — a PCB fault.

Causes, fixes & costs for Baxi E164 → · All Baxi codes

Biasi E164

The E164 fault code on Biasi boilers — sometimes shown as A07 on certain models — indicates a problem with the domestic hot water (DHW) temperature sensor. Specifically, the NTC (Negative Temperature Coefficient) thermistor that monitors hot water outlet temperature has either failed, drifted out of specification, or is sending readings that suggest the hot water temperature has climbed to an unsafe level. When the boiler's control board detects this condition, it shuts the boiler down as a safety precaution, placing it into lockout. Note that E164 also appears on Baxi boilers (which share the same parent group), where it can relate to a hydraulic pressure switch rather than a DHW sensor — always confirm you are looking at a Biasi-specific manual for your exact model.

Causes, fixes & costs for Biasi E164 → · All Biasi codes

Potterton E164

The E164 code appears on Potterton boilers when the control board detects a problem with the domestic hot water (DHW) NTC (negative temperature coefficient) thermistor — the sensor responsible for measuring the temperature of your hot water. The fault can arise from either a short circuit or an open circuit within the sensor itself, meaning the boiler's electronics are either reading an impossibly low resistance (short) or getting no signal at all (open). In some cases the code can also point to an issue with the heating flow sensor or its associated wiring. Either way, the boiler cannot reliably monitor hot water temperature and will restrict or halt operation until the fault is resolved.

Causes, fixes & costs for Potterton E164 → · All Potterton codes

Frequently asked questions

Is the E164 fault code the same on every boiler?

No. E164 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 E164 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 E164 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.