A few weeks ago we switched over to heat from cool We have had an issue since then. The system eventually get to a lockout with comfort alert 3 showing The system is water to air with two zones on this unit and two units on the same closed loop. The second system is running and heating just fine. This is the detail of todays startup after sitting with power off for a full week. Min 0: Power up Heat set to on 58 read 60 set Green and yellow flash Low speed fan running Comfort control solid single green Min 9 - Compressor on Flash just green on front Min 12 - Compressor off line is hot Min 16 compressor on Min 19 compressor off line hot Min 23 compressor on Min 24 compressor off Min 35 compressor on Min 37 compressor off line is hot Min 39 Comfort code 3 flashing (single flashing green front panel, no lockout) temp at 60 Min 41 Moved thermostat to 64 Min 46 compressor on ( code 3 still flashing) Min 49 compressor off Min 53 Compressor On Min 56 Compressor off Min 60 Compressor on Min 62 Compressor off (front panel red flashing low pressure and red flashing water flow) Additional notes: After doing some reading last week I powered off both systems and turned the failing system back to cool and set thermostat to call for cool for 10 min and then powered off for 10 and set to heat. Same eventual issue of lockout comfort code 3 We also have a new filter in the system. This system has been setup to only run the fan on low because high fan was causing too much noise, I run the fan with the On setting at the thermostat.