Error 937 or 2P7: water isn't circulating through the heat pump

What it means

The heat pump heats the water for your heating and sends it to the radiators or underfloor heating. To work, it needs the water to circulate, and it checks this with a flow meter.

If it doesn't detect the flow rate it expects, it stops and shows a warning: 2P7 during the initial check (pre-circulation) and 937 with the unit running.

Most likely causes

1. Closed valves in the system, for example after building work or a repair.
2. Air in the circuit, especially after topping up or after a long period out of use.
3. Low pressure in the water circuit.
4. Dirty filter at the unit's inlet.
5. The pump or the flow meter.

What you can check yourself

Without tools and without opening the unit.

1. Check the system's isolation valves, next to the indoor unit: with the handle in line with the pipe, they're open.
2. Check the pressure gauge on the water circuit with the unit off and note down the reading. If it's low, don't top it up yourself: tell us when you book an engineer.
3. Switch the unit off and back on again, once.

If the warning comes back with the valves open, book an engineer: there's most likely air in the circuit or a flow problem, and bleeding it properly is a job for an engineer.