❗Error code E4
The error code E4 is linked to the water flow in the same way as the PL error.
It generally means that there is enough water flow to actuate the flow sensor, but not enough to prevent the heat exchanger from rising in temperature (and therefore the pressure gauge from rising in pressure).
You will need to make sure that the flow is good, not blocked, and the valve is open.
If this persists, check that the code appears when starting up the pump, or randomly.
If it is random, or in the morning, it must be a flow failure such as poor filtration priming, or an installation fault.
Is your heat pump at the same level / height as the filtration? If not, this is usually the problem. A non-return valve is then necessary.
If the error code occurs as soon as the heat pump is started, the High Pressure and Low Pressure sensors must be checked.
By swapping the two sensors, check if the error code changes. If it changes, then the sensor must be replaced.