There is a "temperature difference" setting available via the menu. The operations manual I have says that this is "The temperature difference between measured water temperature and purpose water temperature" and is use to stop/start the the heating.

The default setting is 9, which gives a 5 deg difference (0.5 degrees increments). Mine is currently set to 8.

I interpret it all of this to mean that if I set my unit to heat the water to 55 degrees, it should, on the default setting, kick in again (timer permitting) when the temperature drops to 50.

But that doesn't seem to be happening. I recently saw the panel indicating that the unit was on, that the temperature was 43 degrees, and yet the compressor was not running.

First question: Do I understand this setting correctly?

Secondly: Which is the more efficient way to operate? Have that difference set low so that the compressor kicks in earlier but, I am supposing, for a shorter period of time?
 

11 hours ago, Bobster said:

that the temperature was 43 degrees, and yet the compressor was not running.

Sometimes there is also a Timer configured, to only allow heating during certain periods. If so then the Compressor will not kick in even if the difference is 20 Degree. 

11 hours ago, Bobster said:

"temperature difference"

Some of the Heat pumps will only circulate the water once the Water in the heat pump is 5 to 7 degrees warmer as the measured water temp in the geyser. I think the setting you are referring to is this setting.  

7 hours ago, Jaco de Jongh said:

19 hours ago, Bobster said:

that the temperature was 43 degrees, and yet the compressor was not running.

Sometimes there is also a Timer configured, to only allow heating during certain periods. If so then the Compressor will not kick in even if the difference is 20 Degree. 

I understand that. It seems to me that there are three states
1) Off (this is forced by the timer, and all you see on the display is actual temperature)
2) On but not actively heating (various icons on the display light up and the display shows the target temperature and the actual temperature)
3) On and the compressor is running (a triangle icon now lights up on the display)

My problem occurs at 2 - the unit is on (it's also in the on period set by the timer), target temperature is 55 but the water in the geyser is 43.

But you're interpretation of the setting is interesting and offers an explanation for what I am seeing. Should I then drop that setting?

57 minutes ago, Bobster said:

My problem occurs at 2

 

57 minutes ago, Bobster said:

Should I then drop that setting?

Depending on the Ambient temp at 2 in the morning, dropping the setting might not help. The COP at very low ambient temperatures are also very low, and lowering the setting might not have the required results. 

1 hour ago, Jaco de Jongh said:

 

Depending on the Ambient temp at 2 in the morning, dropping the setting might not help. The COP at very low ambient temperatures are also very low, and lowering the setting might not have the required results. 

Sorry, Jaco. I meant that my problem occurs at state (2) of the 3 that I listed. The unit is on, the temperature in the tank is down in the 40s, but the compressor isn't running. Generally this is about 6 in the evening. The timer turns the pump back on at 15:30.