How to Replace a Boiler NTC Sensor (UK)
Swap flow, return and DHW NTC sensors on Worcester, Vaillant, Baxi and Ideal boilers. Resistance charts.
Worcester BoschVaillantBaxiIdeal
Sensor readings
NTCs are 10 kΩ at 25 °C, 1 kΩ at 80 °C. Out-of-range values throw F20 / F22 / F28. Test cold before condemning.
OEM part numbers
- Worcester Greenstar — flow/return 87161567160.
- Vaillant ecoTEC — 193586 (single wire clip-on).
- Baxi 800 — 720012801.
- Ideal Logic — 173500.
Fit
Clip-on types just push over the pipe. Screw-in NTCs use a fibre washer — never PTFE.
Frequently asked questions
- What is F20 on Vaillant?
- Overheat safety trip — usually a failed flow NTC reading over-temperature, not actual overheat.
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