Markus heat pump problem

[westray7]

Hi
I have years of experience in plumbing and electrics but little in refrigeration. We have a 2.5kw Markus Ground source heat pump. 10 years old approx. The company went bust years ago. We are on an outer Orkney (off Scotland) island so any engineer visit is expensive. Hence usually need to self fix or replace.
Unit runs but....input to condenser is very hot but very little heat goes into the water. Expansion valve freezing up. Following advice, I have wound its adjustment in and out in case it had stuck. No improvement.
Unit has no gauges etc. There are two gas connection points (for applying gauges also?)
Please any suggestions.

[SteinarN]

It may be low on gas or have a defect expansion valve. In addition the manufacturer installed a to small expansion valve on some R134A pumps causing unnecessarily low evaporating temperature. I suppose your pump has no liquid sight glass. If it dont have one, then the proper procedure is to measure the high pressure, convert it to temperature, measure the condenser refrigerant outlet temperature and fill the system until the pressure derived temperature gets roughly 3 to 4C warmer than the condenser outlet refrigerant temperature.

As you now have tampered with the expansion valve adjustment you have to observe the suction superheat as you fill the system and adjust the expansion valve as required.

If the pressure derived temperature already is warmer, then your expansion valve probably is defect.