Thermostat Upon arrival spoke with customer who believed that issue may have been related to hot surface igniter that was recommended to be replaced. Inspected furnace. No error code @ furnace. Had customer raised temperature @ thermostat to fire furnace. Furnace did not fired after a few minutes. Checked control board voltage to be correct @ terminals. 27 volts between R & Common. Checked between R & W, R & G Bypassed thermostat. Jumped R & W terminals: furnace fires system is on/ running Customer explained that this issue started after batteries were replaced. Removed and installed new batteries. Situation did not change with thermostat. Bypass thermostat @ wire directly and furnace fired. Bad thermostat. Customer gave green light to replace thermostat: Installed new Honeywell T4 thermostat and reconfigured thermostat. Had new thermostat call for heat once more. System is on/ running. Took temperature split and monitor operation: System back up for normal operation @ this time. Vie