P08 on a Grant Aerona 290: Middle pressure protection
Short answer
On a Grant heat pump, P08 means: Middle pressure protection. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Middle pressure protection.
Part involved: middle pressure switch / refrigerant PCB.
Likely causes:
- Middle pressure switch not connected correctly.
- The refrigerant PCB is faulty.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: Not stated in DOC 0204.
Manual reset: DOC 0204 s11.1: once the fault is resolved, reset by turning the unit OFF and back ON; s11.5: power cycle can be done from the Aerona Smart Controller touchscreen instead of the external isolator (installer procedure).
What you can check
- Note the exact code shown on the controller display and tell your installer or Grant-trained engineer.
- Check the heat pump isolator switch and the consumer-unit breaker/RCD for the heat pump are ON (do not repeatedly reset a tripping breaker).
What the engineer will check
- Check connections on sensor and refrigerant PCB; replace middle pressure switch.
- Check refrigerant PCB; replace if faulty.
Who to ask for: Grant-trained heat pump engineer.
Certification: F-gas certified engineer also trained/competent for flammable A3 refrigerant R290 (propane).
What you might notice
Sources
- Grant Aerona 290 Air to Water Air Source Heat Pump Range - Installation & Operating Instructions (UK DOC 0204) ↗ · Rev 1.9 · page 54 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026