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Geothermal system keeps shutting down
Have a 6 year old geothermal system that has been working fine until the start of this month. It keeps shutting down showing a high pressure fault. It is a 5 ton forced air/hydronic with forced air priority. H-O keeps the forced air stats turned off and runs the radiant side with there own stats. Geo system heats a 60 gallon radiant storage tank using a Ranco control with a set point of 100 and a 5 degree DT. Each time the lockout board shows a high pressure switch fault. Continuity test shows switch to be closed. I can reset the system and it will heat the tank up to 100 then start again when the tank drops to 95. I can watch it for an hour as it runs several cycles and everything works as it should. A day or two later I get a call saying it locked out again. Performance when running is excellent, loop side 42 degree entering water temperature, 7 degree DT and 14 gallons of flow. System side shows a 9 degree DT. Pressures are right where they should be and the HE is 47,000 Btu's with a COP average of 4. I've never seen the the system pressure over 275 psi in normal operation. Tech guy says test the switch shut-off pressure and it opens at 625psi. First recommendation was to switch out the lockout board. Did that and same problem. Next step is to add a new pressure switch to the high pressure port using a tee. Anyone out there had a similar problem or any ideas?