Have you noticed ice on your heat pump? It’s actually normal for your heat pump to have ice on it, especially in the wintertime. Since all the heat is being extracted from the outside and being distributed to the inside, the heat pump is going to get condensation on it, and it will freeze if the temperatures are low enough outside.
Once your heat pump ices up, it will naturally go into a “defrost” mode to defrost the ice that has built up. If you do notice that the ice is built up and hasn’t gone away in a few days, then that is an indicator that the defrost board on your heat pump has failed – as it’s not allowing it to go into defrost mode. There are other factors that lead up to built up ice on your heat pump as there are lots of variables that play into its proper function.