A stuck reversing valve usually just needs a tap

To check if your heat pump’s reversing valve is stuck, listen for a click and feel the line temperatures — then you can often unstick it by tapping the valve body with a screwdriver.

The reversing valve is the part that flips your heat pump between heating and cooling. When it sticks, you’ll notice it immediately: the system blows cold air in heat mode, or hot air in cool mode. Sometimes you’ll hear a faint hissing from the valve trying to shift, or the outdoor unit might sound different than usual.

First, confirm the problem. With the system off, remove the access panel and locate the valve — it’s the one with four copper lines connected to it, usually