E3 on an Ideal Heating HP290: Header Thermistor (T1) Error (for Hybrid/Cascade)
Short answer
On an Ideal Heating heat pump, E3 means: Header Thermistor (T1) Error (for Hybrid/Cascade). 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: Header Thermistor (T1) Error (for Hybrid/Cascade).
Part involved: header thermistor T1.
Likely causes:
- User interface settings wrong for non-hybrid/cascade system; header thermistor not connected or wiring loose; thermistor outside 30-500 kOhm; outdoor 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 settings (5.8); connect/secure T1 wiring; measure 30-500 kOhm; replace thermistor or outdoor PCB.
Who to ask for: Heat pump engineer competent with R290 (A3, highly flammable); refrigerant-circuit work requires Cat I/II F-gas plus City & Guilds 6187-21 or equivalent (I&M p.93 warning).
Certification: F-gas Cat I/II + C&G 6187-21 (R290) for refrigerant work; electrical work by competent person.
Sources
- HP290 Monobloc Heat Pump System - Installation & Maintenance (UIN 240080 A09) ↗ · UIN 240080 A09 · page 98 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026