LED-78 on an Ideal Heating Logic Air: Electric expansion valve sensor error
Short answer
On an Ideal Heating heat pump, LED-78 means: Electric expansion valve sensor error. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Electric expansion valve sensor error.
Part involved: expansion valve temperature thermistor.
When it shows: Thermistor short or open detected.
Likely causes:
- 1. Connector connection failure/open 2. Thermistor failure 3. PCB failure (main PCB).
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
What you can check
- Note the code or fault message shown on the controller/Halo and when it appeared; check the heat pump's isolator and consumer-unit breaker are on.
What the engineer will check
- Check connector and cable continuity; disconnect thermistor and check characteristic (Service Parts Information 5); check PCB reference voltage Main PCB PA1:4-6 = 5 V; replace thermistor or PCB.
Who to ask for: Heat pump engineer; casing removal only by persons competent with R32 (A2L); refrigerant-circuit work requires Cat I/II F-gas certification (I&M p.75 warning).
Certification: F-gas Cat I/II for refrigerant work; electrical work by competent person.
Sources
- Maintenance Manual LOGIC AIR 8-10 Air/water heat pump Monobloc system (U0753484_2451_EN_1) ↗ · U0753484_2451_EN_1 · page 21 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026