E154 Boiler Fault Code: What It Means on Every Brand

The E154 fault code appears on 4 boiler brands — Baxi, Biasi, Main and Potterton — and on all of them it points to the same kind of problem. The details still differ by brand (thresholds, sub-codes, reset procedure), so use the table below to jump to the page for your boiler.

Lockout — engineer likely 4 brands use this code

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 E154 means	Severity	DIY?
BBaxi	The E154 code on a Baxi boiler signals that the boiler's internal diagnostics have detected a problem during the flow and return temperature sensor test. Full guide →	Lockout — engineer likely	No
BBiasi	The E154 fault code (sometimes also displayed as A04 on certain Biasi models) indicates that the boiler's control board has not received confirmation that the fan is running correctly. Full guide →	Lockout — engineer likely	No
MMain	When your Main boiler displays E154, it has detected a problem during its internal flow and return sensor temperature test. Full guide →	Lockout — engineer likely	No
PPotterton	The E154 code on a Potterton boiler indicates a primary flow fault — the boiler's control system has detected that water is not circulating correctly through the central heating circuit,… Full guide →	Lockout — engineer likely	No

E154 brand by brand

Baxi E154

The E154 code on a Baxi boiler signals that the boiler's internal diagnostics have detected a problem during the flow and return temperature sensor test. In plain terms, the boiler is checking how quickly the water temperature rises at the flow and return pipes when it fires — if the readings don't match what's expected, or if a sensor is returning an implausible value, E154 is triggered. Engineers sometimes refer to this as a primary flow fault. The root cause is usually either a circulation problem (water isn't moving properly around the system) or a faulty NTC thermistor sensor (the small resistive sensor that measures water temperature). Because the boiler relies on these readings to control firing rate and pump speed, it locks out rather than risk overheating.

Causes, fixes & costs for Baxi E154 → · All Baxi codes

Biasi E154

The E154 fault code (sometimes also displayed as A04 on certain Biasi models) indicates that the boiler's control board has not received confirmation that the fan is running correctly. Biasi boilers use an air pressure switch (APS) — a safety device connected to the fan via heat-resistant venturi tubes — to detect whether the fan is generating sufficient airflow. When the fan spins, the resulting air movement closes the APS, sending a signal to the PCB that ventilation is active and combustion gases can be safely expelled through the flue. If the boiler cannot confirm this — whether due to a failed fan, a blocked flue, a faulty APS, or a wiring issue — it locks out and displays E154 to protect the occupants from potentially harmful gases accumulating indoors.

Causes, fixes & costs for Biasi E154 → · All Biasi codes

Main E154

When your Main boiler displays E154, it has detected a problem during its internal flow and return sensor temperature test. In practice this means the boiler has compared the temperatures measured at the flow (water leaving the boiler) and return (water coming back) pipes and found they are not behaving as expected — either the difference between them is outside normal bounds, or circulation is not performing as it should. This can point to a circulation fault, a failed or inaccurate temperature sensor, an airlock, or a wiring issue between the sensors and the control board. Because Main, Baxi, and Potterton share the same fault code system, E154 has exactly the same meaning across all three brands. The boiler will typically lock out to protect the heat exchanger from overheating until the underlying cause is resolved.

Causes, fixes & costs for Main E154 → · All Main codes

Potterton E154

The E154 code on a Potterton boiler indicates a primary flow fault — the boiler's control system has detected that water is not circulating correctly through the central heating circuit, or that the temperature readings from the flow and return sensors are inconsistent with normal circulation. On some Potterton models this is described more specifically as a flow/return sensor temperature test failure, where the boiler checks the temperature differential between the flow and return pipes to confirm the pump is moving water as expected. Either way, the boiler will lock out as a safety measure until the underlying cause is resolved.

Causes, fixes & costs for Potterton E154 → · All Potterton codes

Frequently asked questions

Is the E154 fault code the same on every boiler?

Broadly, yes — on Baxi, Biasi, Main and Potterton the E154 code points to the same class of fault, and the recommended response is similar. Model-specific details such as sub-codes and reset procedures still vary, so follow the page for your own brand.

Can I fix a E154 fault myself?

Not usually. On every brand listed, E154 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 E154 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.