Return Thermistor Fault error code
Return Thermistor Fault – Keston Heat 45/55 error message
What does Keston Keston Heat 45, 55, 45P and 55P boilers Return Thermistor Fault mean?
Keston documents “Return Thermistor Fault” for Heat 45, 55, 45P and 55P boilers as a fault condition in which the return-temperature sensor or its circuit has failed. This original Heat generation must remain separate from Heat².
The code identifies the condition detected by the product; it does not always identify the failed component on its own. Confirm the full code and exact model before ordering parts or attempting a reset.
The Keston Keston Heat 45, 55, 45P and 55P boilers Return Thermistor Fault error code indicates keston documents “Return Thermistor Fault” for Heat 45, 55, 45P and 55P boilers as a fault condition in which the return-temperature sensor or its circuit has failed. This original Heat generation must remain separate from Heat². This guide explains what the code means, the symptoms and likely causes, the checks that are safe to make, and when to stop and arrange an authorised repair.
Symptoms you may notice
The boiler display shows Return Thermistor Fault. Heating or cylinder-hot-water production may stop, enter a controlled shutdown or lock out until the detected condition is corrected.
Common causes
The return-temperature sensor or its circuit has failed. Depending on the message, the service chart directs checks of system filling and circulation, sensors and wiring, fan, flame proving, gas supply, mains voltage, external interlock, configuration card or main PCB.
Before you start troubleshooting
Use the display, rating label or product menu to confirm the exact model. Similar-looking codes can have different meanings across product generations and regions.
- Record the complete code before switching the equipment off.
- Check only user-accessible controls, filters and external connections described in the manual.
- Do not open gas, refrigerant, combustion or electrical compartments.
Troubleshooting steps
Record the exact “Return Thermistor Fault” message and the operating conditions. The official service chart requires internal diagnostic checks, so do not remove the casing or test components yourself.
Can you fix this error code yourself?
The safest next step depends on the exact model and the cause behind the code. External checks may help, but a returning fault needs professional diagnosis.
A successful reset is not proof that the underlying issue is fixed. If Return Thermistor Fault reappears, note when it happens and give that information to the service engineer.
Reset instructions
Reset once only where the official fault screen or service chart instructs it and after permitted external checks. If Return Thermistor Fault returns, stop resetting and arrange professional diagnosis.
Applicable products and models
Keston Heat 45, 55, 45P and 55P boilersHeat 45; Heat 55; Heat 45P; Heat 55P2018 product generationWhen to contact a professional
Contact Keston while the appliance is under warranty, or a suitably qualified Gas Safe registered engineer (or locally competent person), when the fault persists or returns or when internal testing or repair is required.
Frequently asked questions
What does Keston Keston Heat 45, 55, 45P and 55P boilers Return Thermistor Fault mean?
Keston documents “Return Thermistor Fault” for Heat 45, 55, 45P and 55P boilers as a fault condition in which the return-temperature sensor or its circuit has failed. This original Heat generation must remain separate from Heat².
Can I fix Keston Keston Heat 45, 55, 45P and 55P boilers Return Thermistor Fault myself?
Some external checks may be suitable for the user, but the result depends on the exact model and cause. Use the official manual and arrange service if the code returns.
Should I reset the product after code Return Thermistor Fault?
Reset once only where the official fault screen or service chart instructs it and after permitted external checks. If Return Thermistor Fault returns, stop resetting and arrange professional diagnosis.
When should I arrange a repair?
Contact Keston while the appliance is under warranty, or a suitably qualified Gas Safe registered engineer (or locally competent person), when the fault persists or returns or when internal testing or repair is required.