P03 on a Grant Aerona 290: Low pressure protection
Short answer
On a Grant heat pump, P03 means: Low 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: Low pressure protection.
Part involved: low pressure / refrigerant charge.
Likely causes:
- Lack of refrigerant.
- Refrigerant system is blocked.
- The heat pump is not running in regular operating conditions.
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 outdoor unit air inlet and fan outlet are not blocked by leaves, snow, ice or stored objects.
What the engineer will check
- Check for leak in refrigerant circuit; repair leak.
- Check whether the filter in refrigerant circuit is blocked; change filter.
- Check whether outdoor ambient and inlet water temperatures are normal - if too high or low the unit will stop.
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