1. Are the air intake and exhaust ducts covered, blocked or overgrown?
The intake and exhaust openings on the heat pump must be free, so that the heat pump can “breathe” properly. Increased operating costs (the efficiency of the heat pump deteriorates) and malfunctions can thus be avoided.
2. Is the fan running?
If the fan is not running, the heat pump will not be able to remove the resulting cold air and the air heat exchanger (evaporator) will freeze. The result is a low-pressure fault. To check the operation of the fan, it can be controlled via the heat pump controller. To do this, go to Service > Settings > Vent system and set a check mark at Fan BOSUP. The fan will run immediately after confirmation. It runs for the duration of the time or cset an be stopped manually by unchecking Fan BOSUP. 
ATTENTION: during the EVU lockout period, the fan may not run because the supply voltage has been switched off.
3. Does the outdoor temperature sensor show the correct temperature?
Check the plausibility of the value displayed. This should correspond to the current outdoor temperature and be approximately the same as the heat source inlet temperature. These values can be found under Service > Information > Temperatures.
ATTENTION: the outdoor temperature sensor must be mounted on the northern outer wall of the building and protected from direct sunlight!

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