Samsung air to water heat pump

[aupanner]

I have a problem with a Samgsung RC160 MHX EA air to water heat pump. The fault code was high pressure problem. I fitted my gauges and noticed the low pressure going down to zero. I am assuming the expansion valve is where the problem is and it trips on high pressure as the refrigerant liquid is filling the plate heat exchanger. The number on the expansion valve is SXK 06 and its 12 v dc. My question is how do I find out if the expansion valve is at fault or if its not getting a signal to open? Any help would be greatly appreciated

[Brian_UK]

Have you checked the water flow rate?

[aupanner]

when I saw it was a high pressure fault water flow was my first thoughts. Is there a sensor what would keep expansion valve from opening if not enough water flow? The compressor discharge pipe did not rise above 27c

[aupanner]

The fault code that comes up is E407 which is compressor off on high pressure. I see no other fault codes. When I run unit I would expect low pressure side to run at 80 psi as its on R410, but low pressure goes down to zero.