Andrews E65 Fault Code: Causes, Fixes & Repair Costs
What does the Andrews E65 fault code mean?
E65 on an Andrews water heater means the return temperature sensor circuit has gone open — the control board is getting no reading at all from the sensor that measures water temperature returning to the heat exchanger. An open circuit is typically a broken wire, an unplugged connector or a failed sensor element. Because the control strategy relies on comparing flow and return temperatures to modulate the burner safely, the unit will not run normally without this reading: it blocks operation and displays E65 until the circuit is restored. The companion code E75 is the same sensor shorted rather than open — between them they distinguish the two ways the circuit can fail.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Failed return sensor (NTC) Common
Thermistors age in the hot, damp conditions of a plant-room water heater and eventually fail open. The board sees infinite resistance — no reading — and raises E65. Replacement of the sensor restores normal operation.
- Broken wiring or unplugged connector Common
The sensor lead runs through the appliance to the control board; a chafed wire, a connector disturbed during maintenance or corrosion in the plug gives the same open-circuit signature as a dead sensor. Engineers check the wiring before condemning the sensor.
- Control board input fault Rare
Rarely, the sensor and wiring test fine and the fault is the measuring input on the PCB itself. That is diagnosed by measuring known-good sensor resistance at the board connector.
How to fix it
- Note the code and any recent work on the unit DIY safe
If E65 appeared right after a service or plant-room work, a disturbed connector is the prime suspect — say so when booking the engineer.
- Reset once if the unit offers it DIY safe
A single reset confirms whether the circuit fault is constant or intermittent. If E65 returns immediately, the reading is genuinely absent and the unit needs attention.
- Leave sensor and wiring checks to an engineer Gas Safe engineer
Testing the return NTC means resistance measurements against the temperature table in the service manual, inside a commercial gas appliance. A commercially qualified Gas Safe registered engineer will test the sensor, the loom and the board input in that order.
- Engineer: replace the sensor or repair the circuit Gas Safe engineer
The usual outcome is a new return sensor — an inexpensive part — or a repaired connection. If the board input itself has failed, the PCB is replaced. Either way the engineer should verify flow/return readings track correctly before leaving.
Parts you may need
- Return temperature sensor (NTC) · from £35
- Sensor wiring loom · from £40
- Main control PCB · from £320
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£320, depending on the underlying cause.
Frequently asked questions
What is the difference between Andrews E65 and E75?
Same sensor, opposite failures. E65 means the return temperature sensor circuit is open — no reading at all, usually a failed sensor or broken wiring. E75 means the circuit is shorted — a reading pinned at an impossible value, usually a shorted sensor or crushed lead. Both stop the unit running normally until fixed.
Is E65 urgent?
It disables the water heater, so in a commercial building it is urgent in practical terms — no stored hot water — even though the fault itself is a benign sensor failure rather than a safety event. The repair is usually quick and inexpensive once an engineer is on site.
Can I replace the return sensor myself?
No. It sits within a commercial gas appliance and the work must be done by a Gas Safe registered engineer with commercial scope. It is, however, one of the cheaper and quicker repairs on these units.