Potterton E20 fault codewhat it means and how to fix it
Central 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.
Take care
Get a Gas Safe registered engineer to look at your Potterton E20
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 the boiler still make hot water?
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, but no heating
Consistent with the heating flow sensor alone.
Engineer; a short visit.
Nothing works
The sensor is in the common flow path; expected.
Engineer.
What E20 means
E20 opens every Potterton table from the 2007 Gold Combi HE to the 2019 Assure: "Central Heating NTC Fault". The NTC is the thermistor that reads the heating flow temperature, and the boiler stops when its reading is impossible — open circuit or short.
Potterton's user guides file E20 with E28, E50, E125 and E160 as the component faults, where the owner's only job is to write the code down and ring the installer. The installation manuals confirm it is a component code, and fault-finding section E gives the bench test: a sound sensor reads roughly 10 kΩ when cold at 25 °C and its resistance falls as it warms, so anything wildly off that curve is replaced.
On the Assure and Promax Ultra the number is 20, it is shown with the spanner rather than the R — the installer manuals say "followed by 20, 28, 40, 160 or 321 indicates possible faulty components" — and it is not on the reset list. The sensor is cheap and the job is short; the reason it fails is usually a connector or a lead rather than the thermistor itself, which is why a good engineer checks the plug before fitting a part.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Sensor lead or connector | A plug off or corroded at the sensor or the PCB reads as open circuit. First check on the chart, and the most common finding. | Common |
| Thermistor failed | Out of range against the 10 kΩ at 25 °C figure. On the Assure the flow and return sensors are one spare (7207471); on the Promax, "NTC Sensor" 5114725. | Common |
| PCB input | Rare; suspected only when a new sensor and a good lead still show E20. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£50–£120
Time on site
30 minutes
Sensor and fitting £60–£110. Connector repair at a call-out £60–£90.
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
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Potterton fault codes
- 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
- E154Get it checkedFlow/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.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.