L6 on a Grant heat pump: Flow switch error
Short answer
On a Grant heat pump, L6 means: Flow switch error. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 2 sources
What it means
The manual says: Flow switch error.
Part involved: flow switch / pump / water circuit.
When it shows: Chofu: flow switch open for 2 min, or 5 retries within 60 min, stops the compressor; errors 1-4 auto-restart and are only logged in history; 5th requires manual reset.
Likely causes:
- Clogged water pump and/or water circuit.
- Flow switch 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: No.
Manual reset: Engineer: press - and + on the master remote controller for 3 s, or Reset SW on PCB(Terminal).
What you can check
- Note the exact code shown on the controller display and tell your installer or Grant-trained engineer.
- Grant advises homeowners NOT to reset Aerona3 fault codes themselves - leave the reset to the 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.
What the engineer will check
- Check the pump and the water circuit; remove obstructions, clean the water filter, unblock the pump.
- Otherwise replace flow switch.
Who to ask for: Grant-trained heat pump engineer.
What you might notice
What owners and engineers report
11 owner and engineer reports mention this.
- No heating on the Aerona³ R32: 5 reports
- No hot water on the Aerona³ R32: 4 reports
- Keeps stopping / cutting out on the Aerona³ R32: 1 report
- No heating on the Aerona³ (R410A): 1 report
Sources
- Chofu Service Manual AEYC-0643XU-CH / 1043XU-CH / 1242XU-CH / 1643XU-CH (RA-98(5)) - Air to Water Heat Pump, Monobloc DC Inverter ↗ · RA-98(5) · page 30 · Reviewed 23 September 2026
- Chofu AEYC-0639U-CH / AEYC-1039U-CH / AEYC-1639U-CH Installation and Instruction Manual (R410A) ↗ · Chofu AEYC-0639U/1039U/1639U-CH Installation and Instruction Manual (ManualsLib-derived copy) · page 145 (flow-switch logic p78) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026