For about a 2 years now we have had our DHW disconnected from our geothermal furnace because the lines were leaking, the holding tank needed replaced, and it was a low priority. This last weekend I plumb a new tank back in our DHW. The furnace feeds a 50gal holding tank, which feeds the houses 105gal actual hot water tank.
I noticed immediately from my monitoring software that it was behaving differently than I remember from the past. I did some investigating and found that the DHW pump was not turning on. Looking further I see that the control board enables power to the pump, but that it then goes through a pair of "safety snap" sensors.
One of them is located on the incoming water line from the holding tank (presumably to limit how hot the incoming water temp is as to not go above some safe limit). It is a normally closed switch that will open once the water temperature is over some limit. It is working as expected.
The second sensor/switch is located on the hot side of the compressor and I assume is there to be sure that running water through the desuperheater only happens once the high pressure temperature of the desuperheater is high enough to make it worth it, and also prevents DHW from dumping heat into the system instead of taking it out. This switch is normally open and at 125* closes. This switch is the "culprit". I pulled it out and using hot water was able to confirm that it does actually work as it should when the water is >125*.
I measured the high pressure line from the compressor, where this switch is located and see that it is only reaching 117*, which isn't enough to trigger the switch.
SO ultimately my DHW is not working because the compressor line is not getting hot enough to activate the safety circuitry to turn on the DHW pump.
Below is a capture of my system monitor:
The red line shows the [CURRENT] hot water out from the DHW, it rises and rises because heat is creeping its way from the desuperheater up through the to the sensor on the return line, but the pump is never turning on. I added the purple line as a representation of what [SHOULD/used to] happen when it was working: The system would turn on, heat would creep up like now, but at some point (quickly) the hot side of the compressor would reach a hot enough point to activate the switch and turn on the pump, at which time the water would run through the desuperheater evacuating the heat to the the holding tank and would continue to do that until the system finished its cycle, adding maybe 5* delta the whole time (above the blue line).
Any advice on what would cause the output high pressure side of the compressor for the DHW desuperheater to not be reaching the appropriate temperature?
5 Ton Heat Controller (Comfort Aire) closed loop ground source heat pump. 2 Stage scroll compressor. Model#HTV060A1C01JLM
Thanks in advance.