Hi,
Any poor electrical connections around your thermostat between it and
furnace? Furnace has safety shut down sensor(when it gets TOO hot).
maybe this thing is acting up?
I never saw this sensor gone bad tho.
Tony

Frontier wrote:

I am having trouble with keeping the heat on in our home. The heat will
come on, as normal, but the blower and heat will shut down before reaching
the temperature at which the thermostat is set and the thermostat continues
to flash "heat" as if it thinks the unit is still on. This normally happens
when the outside temperature gets below about 20 F.

We called in the heating people and they determined that the valve was shot
from doing a test that showed that little gas was getting to the furnace.
This was right after Thanksgiving. We had a warm spell and it seemed to be
working OK, but the last few days have been colder and it is happening
again.

The odd thing is that sometimes it will run for hours and work fine, as
happened last night. I got up during the night to find the temperature in
the house at 64. I turned the heat off (to reset the thoermostat) and back
on and it ran for a number of hours.

Just a few minutes ago I turned it on after replacing the filter, and it ran
for about 10 minutes before shutting off, with "heat" still flashing on the
thermostat.

Any ideas?