UK trade guideBoiler Spares 5 min readUpdated 11 July 2026

How to Replace the Ntc Sensor on a Ideal Logic Plus 24 (UK)

Step-by-step UK guide to replacing the flow / return / DHW thermistor on a Ideal Logic Plus 24. Part numbers, torques, commissioning.

Ideal

The part

Replace an NTC thermistor on Ideal Logic Plus 24 for wildly inaccurate flow temps or an F22/F75/L1 low-water fault.

Isolate safely

Each NTC on Ideal Logic Plus 24 clips onto the copper flow pipe with a spring clip. Fit fresh heat-sink compound before refitting.

Fit and commission

Cross-check resistance with a multimeter — 10 kΩ at 25 °C for standard blue-body NTCs.

Recommission checklist

Refill the Ideal Logic Plus 24 to 1.2 bar cold. Bleed high-point radiators and the internal AAV.

Run a full flue-gas analysis after 15 minutes. Log the reading against the OEM commissioning envelope in the Benchmark book.

Frequently asked questions

Which colour?
Flow NTC is normally blue, return NTC red on Ideal Logic Plus 24. Do not swap.
Wire polarity?
NTCs are non-polar — but keep leads clear of ignition HT leads.
Do I need to notify the manufacturer?
Only if the Ideal Logic Plus 24 is in warranty — Ideal require log of any part swap for labour claims.
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