RETURN THERMISTOR FAULT error code
RETURN THERMISTOR FAULT – Keston Combi C30/C35 fault
What does Keston Keston Combi C30 and C35 combination boilers RETURN THERMISTOR FAULT mean?
Keston documents the display message “RETURN THERMISTOR FAULT” for the 2018 Combi C30 and C35 range as return-temperature sensor fault. This product predates Combi² and must remain a separate product identity.
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 Combi C30 and C35 combination boilers RETURN THERMISTOR FAULT error code indicates keston documents the display message “RETURN THERMISTOR FAULT” for the 2018 Combi C30 and C35 range as return-temperature sensor fault. This product predates Combi² and must remain a separate product identity. 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; central heating or domestic-hot-water operation may stop or lock out until the condition is corrected.
Common causes
The message is associated with return-temperature sensor fault and the related pressure, temperature-sensing, fan, ignition, flame, electrical-supply or controller circuit.
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
Contact a qualified engineer to diagnose the return-temperature sensor fault using the product-specific service documentation.
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
Follow the display instruction and press Restart once only where offered. If the message returns, stop and arrange professional diagnosis.
Applicable products and models
Keston Combi C30 and C35 combination boilersCombi C30; Combi C352018 product generationWhen to contact a professional
Contact a suitably qualified Gas Safe registered engineer when the message persists or returns, or when diagnosis requires internal measurements, wiring checks or replacement parts.
Frequently asked questions
What does Keston Keston Combi C30 and C35 combination boilers RETURN THERMISTOR FAULT mean?
Keston documents the display message “RETURN THERMISTOR FAULT” for the 2018 Combi C30 and C35 range as return-temperature sensor fault. This product predates Combi² and must remain a separate product identity.
Can I fix Keston Keston Combi C30 and C35 combination 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?
Follow the display instruction and press Restart once only where offered. If the message returns, stop and arrange professional diagnosis.
When should I arrange a repair?
Contact a suitably qualified Gas Safe registered engineer when the message persists or returns, or when diagnosis requires internal measurements, wiring checks or replacement parts.