I've got a ClimateMaster 5-ton water-to-water system that's under performing and tripping fault 4. System: Location is Seattle WA area, installed 2015 (this is it's 3rd winter). ClimateMaster 5-ton TMW-060. Source loops are six, 600ft long, 3/4" diameter horizontal loops buried 4ft and 8ft. Source circ pumps are two Grundfos UPS26-99FC (running on high). System feeds a GeoStore 80gal buffer tank. Circ pump from buffer to tmw is a Grundfos UPS 26-99FC (running on low). Load side is twelve, 300ft long, 1/2" diameter pex runs. Load circ pumps are two Grundfos UPS15-55SFC (running on low). All loops (source and load) terminate at manifolds indoors in the utility room. Performance (heating mode): Source pressure drop across the heat pump is 5psi, tables show 13GPM. Source temp drop is 4F (source in 43F, out 39F). Load side temp gain (going into buffer tank) is 5F running at 9GPM. Buffer tank is currently set at 90-100F. Using (delta T) x (flow GPM) x 485 = 25,220 Mbtuh The TMW 060 manual for these conditions shows 39,800 Mbtuh target which puts me at 63% of peak efficiency. Faults: The system has repeatedly tripped fault code 4 (low water coil temp). I've verified function of the thermistor by hooking up a thermocouple in the same location. The thermocouple drops below 10F for several minutes after startup and then stabilizes at 11-12F. Sometimes the unit will run, but mostly it will trip with this low temp. JW3-LT1 jumper is clipped, source loops have methanol freeze protection. I haven't yet re-verified protection level since install in 2015. I can get the system to run by disconnecting the low water temp thermistor and monitoring my thermocouple to ensure it stays just above 10F, but it's making me nervous. Even if it runs, the poor performance is telling me something... but what? I'm only guessing at this point. Any suggestions from the community on things I can check? Any recommendations for tech/service in the greater Seattle area? Thanks in advance!