Baxi E154 fault codewhat it means and how to fix it
Flow and return sensor temperature test failed — the two readings do not make sense together. Usually a sensor or its plug, sometimes poor circulation. Engineer diagnosis.
Take care
Get a Gas Safe registered engineer to look at your Baxi E154
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What E154 means
E154 appears in the 600, 800, Compact and Duo-tec 2 tables as "Flow / return sensor temperature test" and on Baxi's professional page as "Plausibility test (flow/return)". The boiler has two thermistors on the primary circuit, one on the flow out of the heat exchanger and one on the return into it, and the board compares them constantly. It expects the flow to be warmer than the return by a sensible margin when the burner is on, and the two to converge when it is off.
When the readings fail that logic — return hotter than flow, a difference too large to be real, or a sensor jumping about — the board cannot trust either and shows E154. It is not in Baxi's list of codes that can be relit by the Reset button, and it shows with the spanner symbol, so the user guide's instruction applies: contact your installer, annual service provider or Baxi Customer Support.
For an engineer the 600 Combi flow gives the test: the CH sensors read about 10 kΩ at 25 °C and the resistance falls as they warm, so a sensor that reads open, shorted, or wildly different from its partner at the same temperature is condemned, and the two are the same part (Baxi 7207471, "flow sensor and return sensor") on the 600 and 800. The other possibility, less common, is that the sensors are right and the water really is behaving oddly — a return hotter than the flow can happen when the pump has stopped and the exchanger is warming the pipe backwards, or when the diverter has left the circuit half open.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Flow or return thermistor drifted or failed | The most likely cause. Baxi's test is about 10 kΩ at 25 °C, falling with temperature; a sensor well off that at room temperature, or open circuit, fails the plausibility test against its partner. | Common |
| Plug or wiring on one sensor | A corroded connector or a chafed wire gives an intermittent reading that the board sees as a nonsensical difference between flow and return. | Common |
| Sensor out of its pocket | A clip-on sensor that has been disturbed during a service reads the air rather than the pipe, lagging its partner by tens of degrees. | Occasional |
| Genuine reverse or stalled flow | A stopped pump or a diverter stuck between ports can make the return sensor read hotter than the flow. The sensors are telling the truth and the circulation is the fault. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£80–£320
Time on site
45 minutes
Sensor (Baxi 7207471) fitted £80–£130. Wiring repair within a service call. Pump if that is the cause £200–£320.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Baxi / Potterton / Main NTC temperature sensor (flow, return or DHW)
7207471£18–£45Authorised Baxi parts distributor
Price checked 28 September 2026
Baxi / Potterton / Main pump assembly
7684006£120–£240Authorised Baxi parts distributor
Price checked 28 September 2026
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Related Baxi fault codes
- E20Get it checkedCentral heating flow thermistor open or short circuit. Baxi list E20 as a faulty component on every generation, with no householder reset; a cheap sensor swap for an engineer.Related: temperature sensors
- E.04.01Get it checkedFlow temperature sensor short circuit (E.04.01) or disconnected (E.04.02) on the Baxi 200/400 Combi and Combi 2. A sensor or its plug; Baxi's remedy is check the connection, then the sensor.Related: temperature sensors
- E40Get it checkedReturn thermistor open or short circuit on the digital-display Baxis. Spanner symbol, no householder reset, and the same inexpensive sensor as the flow side.Related: temperature sensors
- E50Usually simple to fixHot water thermistor fault on the selector-switch Baxis, shown as E then 50. Heating usually carries on; hot water is unreliable until the sensor is changed. Digital-display combis show E321 instead.Related: temperature sensors
- E321Usually simple to fixDomestic hot water thermistor fault on the digital-display Baxis (shown on some as 163). Heating normally continues; tap temperature control is lost until the sensor is replaced.Related: temperature sensors
- E133Get it checkedBaxi's ignition lockout: "the gas supply has been interrupted, ignition has failed or the flame has not been detected". Check the gas is on, reset once. If it returns, stop.Related: same brand
Own a Baxi boiler? Save it and its codes come first next time.
Related guides
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
- Manufacturer support portal
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.