E5 on an Ideal Heating HP290: Outdoor Unit, Air to Refrigerant Heat Exchanger Outlet Thermistor (T3) Error
Short answer
On an Ideal Heating heat pump, E5 means: Outdoor Unit, Air to Refrigerant Heat Exchanger Outlet Thermistor (T3) 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: Outdoor Unit, Air to Refrigerant Heat Exchanger Outlet Thermistor (T3) Error.
Part involved: T3 thermistor.
Likely causes:
- T3 not correctly connected to outdoor PCB; thermistor outside 6-100 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 connection (Fig 61); measure 6-100 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 100 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026