Why is my LAxx or SIxx heat pump saying “Hot Water Fault”?

Modified on Tue, 29 Nov, 2022 at 2:08 PM

“Hot Water Fault” means that the heat pump could not raise the hot water tank temperature to at least 35C using just the compressor (which it should be able to do in normal circumstances. 

• The installer or a local plumber should be called out to check that there is no air in the pipework or the coil of the cylinder, slowing down the flow of water between your heat pump and the cylinder. The system pressure of the water in the pipework should be between 1.0 and 1.5 bar.

• They should check the circulation pumps all work correctly, and are set to run at a suitably high speed

• They should check that any check valves or 3-port valves installed are opening and closing correctly.

• They should check the temperature probe on the side of the cylinder is positioned correctly on the tank and that it is reading the correct tank temperature.

Once all these checks have been performed, the heat pump’s “Hot water performance” memory should be reset (Hold down MENUE + ENTER button, then go to Settings -> 

Hot Water – Reset Max HP and select Yes). This forces the heat pump to re-learn not hot it can raise the tank temperature using the compressor alone.

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