Potterton E154 fault codewhat it means and how to fix it
Flow/return sensor temperature test on the Potterton Assure and Promax Ultra: the two heating sensors disagree with each other or with physics. Usually circulation; sometimes a sensor.
Take care
Get a Gas Safe registered engineer to look at your Potterton 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.
Does 154 appear with any other code?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
Yes — 109, 125 or 270 as well
Circulation. The sensors are telling the truth.
Engineer; pump and system check.
On its own
A sensor or its wiring is the more likely.
Engineer; a quick resistance test settles it.
What E154 means
The Assure and Promax Ultra tables list "154 — Flow / return sensor temperature test", and the name is the whole of what Potterton say about it. The boiler has two NTC sensors on the heating circuit, flow and return, and it compares them continuously: the return should not be hotter than the flow while the burner runs, the gap between them should not exceed a design limit, and both should move when the pump starts.
When the comparison fails the boiler stops and shows 154 without the R symbol; it is not on the reset list in either manual. Two things produce a failed comparison. The first is water that is not moving properly — the same pump, air and sludge trinity as 109, 125 and 270 — because a stalled flow lets the sensor nearest the burner run away from the other. The second is a sensor that is wrong: drifted, scaled over, loose in its pocket, or with a poor connection.
The Assure lists the pair as a single spare, "Flow sensor and return sensor" (7207471), and the Promax fault-finding figure for the family gives the test — about 10 kΩ at 25 °C, falling as it warms. Because the code cannot itself say which of the two it is, the engineer's first check is the simplest: is the pump running and is the system full.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Poor circulation | Pump, air lock or sludge makes the flow sensor race ahead of the return. If 154 alternates with 109 or 125 this is the cause. | Common |
| Sensor drifted or badly seated | A clip-on sensor that has worked loose from the pipe reads the air; a scaled immersion sensor reads late. | Common |
| Connector or wiring to a sensor | The two sensors share a loom; a poor crimp on one produces an impossible pair of readings. | Occasional |
| Reverse flow | The Assure Heat manual lists "reverse flow through boiler" for its sensor error; on a system boiler with an external pump or a badly set bypass, water can run the wrong way. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£50–£300
Time on site
45 minutes
Sensor £60–£110 fitted. Pump £180–£300.
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 Potterton fault codes
- E20Get it checkedCentral heating NTC fault on every Potterton code display — the flow temperature sensor is open or short circuit. The user guide says note the code and call; no reset is offered.Related: temperature sensors
- E50Get it checkedHot water NTC fault on rotary-switch Potterton combis — Promax Combi, Titanium, Gold Combi, Store, Heatmax. The domestic hot water sensor is open or short. Note the code and call.Related: temperature sensors
- E321Get it checkedHot water NTC fault on the Potterton Assure Combi and Promax Ultra — the digital-display successor to E50. Shown with a spanner; hot water stops, engineer needed.Related: temperature sensors
- E40Get it checkedCentral heating return NTC fault on the Potterton Assure and Promax Ultra. The return sensor is open or short. Shown with a spanner; engineer.Related: temperature sensors
- E119Get it checkedThe sealed system on a rotary-switch Potterton — Promax, Titanium, Gold, Heatmax — has dropped below half a bar. The window shows E1 and then 19. Fill to 1–1.5 bar and it clears itself.Related: same brand
- E133Get it checkedGas supply interrupted, ignition failed or no flame detected — every Potterton generation. Confirm the gas supply, one reset (5 s on the knob, 1–3 s on the button), and call if it returns.Related: same brand
Own a Potterton 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
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.