Upon arrival customer stated that heat was not working for the home and that breaker was tripping. After inspection of 4 year old heat pump system. Found that the breaker was tripped and that disconnect wires had burnt up. Advised customer that disconnect would need to be replaced in order to restore power back to system. Advised customer that unit could have other issues but until power is restored can not tell at this time. Installed new disconnect and found that breaker was still tripping. Breaker was bad, advised customer and customer approved to have changed today. Changed breaker and power began working with system, tested system and noticed that zone board and thermostats were having issues. The downstairs thermostat when calling for heat and you raise temperature 1 degree the emergency heat would activate and the outdoor unit would turn off. When the upstairs would call everything would work like normal. Advised customer that zone board and thermostats are bad and would need to