Check these first, whatever the brand
- Check the water pressure
Daikin and Mitsubishi both look for at least 1 bar. If the pressure is low, ask your installer how to top up, or to do it for you.
- Check the valves are open
Daikin UK says to check the shut-off valves when there's a flow fault. Make sure the valves on the pipes to the heat pump are fully open.
- Listen for gurgling
Air in the system cuts the flow. If you have radiators and hear gurgling, bleeding them can help.
- Give it a moment, then reset once
Some flow codes clear themselves: Daikin says 7H-01 resets automatically after a while. Otherwise reset once at the controller.
- Keep it switched on
In cold weather, leave the heat pump powered. Mitsubishi and Vaillant both say frost protection doesn't work while the unit is off.
When it's time for an engineer
If the code keeps coming back, your installer will check the filters and strainers, purge trapped air, and test the pump and the flow sensor.
Parts people end up buying
Only once the checks point to a part. Match it to your model number: it's on a label on the rating plate on the outdoor unit, and on the indoor unit or cylinder.
- Radiator bleed keySearch on Amazon
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Questions people ask
Why does my heat pump say low flow?
Not enough water is moving round the heating circuit. The makers' lists start with low pressure, air in the system, a closed valve and a blocked filter or strainer, then the pump or flow sensor.
Which code is low water flow on my heat pump?
Mitsubishi Ecodan shows L9, Daikin Altherma 7H-01, Samsung EHS E911 and Vaillant aroTHERM plus F.788 for a pump fault.