Heat Pump Heating Checks: Thermostat, Aux Heat, Pressures

Thermostat configuration is the first thing to check and the most common cause of a heat pump that won’t heat. The AC runs fine all summer, then the first cold night shows a setting that was configured wrong. Bryan explains why the thermostat should be part of every maintenance visit.

Next is the reversing valve. On most systems, the reversing valve must be energized or de-energized correctly for the system to switch into heat. Hearing the valve click isn’t enough. A valve can’t actually shift without a pressure differential, so the compressor has to be running. Bryan’s practical approach: use thermostat service mode if you have it, run the system in heat for a couple of minutes, and confirm the valve really shifts.

Aux heat comes next. Auxiliary heat should run as little as possible, or customers will see high heating bills. The time it matters most is defrost, when the system switches into cooling mode and blows cold air through the house. That’s when the nuisance calls come in. Bryan explains why making sure the heat strips come on and go off matters more to him than testing defrost on every visit. He also shows his preferred test: power the W call from the outdoor unit with a simple jumper, which also confirms the white wire has continuity between the indoor and outdoor units.

Finally, heat pump pressures in heating mode. Bryan covers where to connect your gauges (the common suction port between the reversing valve and the compressor) and the number one mistake techs make. Low suction pressure in heat mode doesn’t automatically mean the system is low on charge. The colder it is outside, the lower the suction will be. 40°F outdoors in heating is like 40°F return air in cooling. High head pressure in heat mode is usually an airflow problem, not a refrigerant problem, so confirm the airflow before you blame the charge. measureQuick has a heat pump heating mode that flags these readings for you.