I have a gen 3 Nest thermostat that replaced a battery powered 2 wire Honeywell unit. I installed the Nest using the existing wires and the furnace worked properly. The next morning the battery was completely drained. I charged it using the USB port and it functioned properly again until the battery ran down. I installed a C wire from the common terminal on the 24 volt transformer on the furnace that powers the zone valves. Checking the new arrangement, I get 24V or thereabouts, from R to C and ) volts from W to C, which I understand is correct. Battery reads 3.771 volts, VOC varies but is currently 25.2, VIN is 25.2 and lin reads 200 Ma (c). When I turn up the thermostat to call for heat, I get the 3 minute delay message. When the timer has expired, the dial briefly turns red calling for heat, but the 3 minute delay message is displayed again. This thermostat is on the first floor. The second unit that controls the heat upstairs and the AC for the entire house is working fine. Voltage on that unit is almost 3.9 and no delay messages are being displayed. Any thoughts as to what might be going on here? Thanks!
