Water dripping from underneath heat pump
Water may collect in the bottom tray of the heat pump. This is due to the normal operation of the heat pump system. There will be a small drain elbow supplied with the unit that should be fitted underneath the unit. 
No hot water and the heat pump is not running
Check that the isolation switch and/or circuit breaker are switched on at the switchboard and check that the fuse is pushed in correctly. If the circuit breaker is tripped or the fuse is blown a service call should be booked. 
Fan changes speed
It is normal for the fan speed to change depending on the ambient temperature and it can stop completely. This is to optimise the performance of the heat pump. 
Heat pump is not running
The unit maybe wired up to Off-Peak tariff and it will only run when supply is available. If you require hot water press the red boost button on the side of the heat pump. This will activate the element in the storage tank for 22 hours.
Heat pump won't start straight away after power is turned back on after a long break
The unit will not start for approximately 3 minutes as the unit does a self diagnostics check. 
Power is available to the heat pump but the unit is not running
The heat pump may have shutdown due to a fault condition. Turn power off to the heat pump for a few seconds and then power it back on. This may reset the heat pump from a protection mode (due to a power surge etc). 
A hissing noise coming from the heat pump unit
This is a normal operational noise from the heat exchanger and occurs when the temperature changes inside the unit with expansion and contraction. 
Heat pump won't start straight away after power is turned back on after a long break
The unit may be connected to Off-Peak supply and the hours of operation are restricted to certain time or times of the day (Off peak 1 is 8 hours and Off peak 2 up to 18 hours).