Ritetemp is a cheap HP thermostat seen in big box stores. And is known to be problematic. Install a HW Mdl 8320 or 8321 depending on your location. One has an overcooling feature for handling humidity, the other does not. You can find them on Ebay at reasonable prices.

IMO

>in cold weather it runs for hours struggling and not calling for the aux heat like the original did

If it is running continuously, but still maintaining the setpoint, that's a GOOD thing. It is not "struggling" it is working as it should. The heat pump is so much more efficient than the aux heat that it is more economical to run it continuously than run the aux heat strips in bursts.

That said I am not a fan of Ritetemp thermostats at all, Honeywell makes better quality ones that do a better job controlling the system, in my opinion. They use a proprietary algorithm that is significantly more complicated than just a timer, or number of degrees difference from setpoint.

"Posted by hvtech42
Honeywell makes better quality ones that do a better job controlling the system, in my opinion. They use a proprietary algorithm that is significantly more complicated than just a timer, or number of degrees difference from setpoint."

I think I would rather have this type of algorithm than just dropping 2 degrees to call for the aux heat. I would hope the HW RTH 3100C would incorporate this since it is specifically made for heat pumps w/ aux heat and I don't need or want a programmable tstat. Do you know about the HW RTH 3100C?

I've never worked with that particular thermostat, but looking through the install manual, the options look very similar to their higher end thermostats, and there is no place to set a degree swing. So yes, I'll take an educated guess that it does use that algorithm.