[KZoltek]

Basically, prior to calling out a service technician (who is scheduled for this Saturday), wished to know if there is anything else I can do to troubleshoot the situation to at least aid the tech in narrowing down the issue?

Have 2-zone heating with heatpump in the attic and multi-stage gas heater on the 1st floor. Have a honeywell heatpump thermostat installed and attached to the heatpump which has worked for approx 360 days without issue. Believe the HP to be 80% efficient.
It's as old as the house which is exactly 4 years and 2 months old.

When I came home from this past weekend the upstairs was recording a temp of 98 degrees. Attempting to shutoff the HP at the thermostat failed to produce results. Changing it to cool air and adjusting temp failed to produce results. Turned off HP at the breaker box and installed a new thermostat (also honeywell) believing that maybe the controller failed. Turned on HP at breaker box after installation (swap-out) with no success. Same problem. Read about "lock-out" and though not quite understanding the specifics - turned off HP at breaker and let the temp come down to 66 degrees with no change in success rate.

Also changed out all filters just in case.

Having read as much as could be found on the net and checking with other homeowners I've got a hypothesis that it's a circuit board on the HP that is not accepting relayed commands from the thermostat. Whether that's because of a soft or hard lockout I don't know... since I'm not an expert.

[NorthernHeat]

A heat pump would have a very hard time reaching a temperature that high. You don't have a zone system, just two systems independent of each other. The heat pump efficiency is measured by SEER the furnace is 80%, the furnace is you aux/emergancy heat source. Hard for me to say why unit won't turn off without checking some voltages throughout system. I think the furnace in attic to be the cause not the outside heatpump unit.

[T-Top]

It sounds like you have a heat sequencer stuck. If it is stuck in the close position the blower and heat strips will keep running even if the thermostat is off.