I have a Heil heat pump. During most of the winter, it works fine. At the tail end, though, around this time of year, the heat strips don't work properly. When using auxiliary/emergency heat, the strips will heat up for about 5 minutes or so, then shut off, and not come back on. If I turn the unit off and then back on, it'll do the same thing. They will heat up for a few minutes, then no more. During the rest of the winter, they do fine, even if running constantly on emergency heat. After summer, it works fine until right around the last cold spell of winter. This causes the house to cool down, of course, and then the thermostat just tries to run auxiliary heat, so basically no heat. This has been happening for the last couple of years. I replaced the thermostat the first time it happened, but it still does it. I have also tried turning it off for a day or so, but that didn't help either. Any ideas or help with this would be much appreciated.