P01 on a Grant Aerona 290: Water flow protection
Short answer
On a Grant heat pump, P01 means: Water flow 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: Water flow protection.
Part involved: flow switch / water circuit.
When it shows: Circulating flow <8.3 L/min; flow through flow switch <4.6 L/min.
Likely causes:
- Lack of water in water system.
- Water flow switch is faulty.
- Water system is blocked.
- Air in system.
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 heating system pressure gauge (if one is fitted) and report a low reading to your installer; make sure the filling loop valves are closed.
- 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 system water pressure and fill to correct pressure.
- Check whether the water flow switch is damaged/faulty; replace if faulty.
- Check if the filter is blocked; clean or change.
- Purge air from the system (Pump purge function via Smart Controller, s11.3).
Who to ask for: Grant-trained heat pump engineer.
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, 57 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026