Open loop, radiant floor. Ran perfectly for two seasons. Ran fine first time this season. Now, goes directly to Fault Retry (slow flash) as soon as heat is called for.... even before compressor runs or valve opens. Fault code is high pressure lockout code 2. Turning off call for heat goes back to solid green light/normal. I am able to get it running by resetting breaker, going into test mode, and calling for heat. Runs fine, goes out of test mode in 20 minutes , and runs fine for hours until I turn it off. Any ideas would be greatly appreciated! Thanks!