The two things come to mind are bad thermostat, or a bad contactor
(relay) in the furnace. Couple years back, some friends of mine had a
furnace that would heat the house up into the 80s, and would not turn
off. They had replaced the thermostat four times, no joke. The problem
turned out to be a bad relay

--

Christopher A. Young
You can't shout down a troll.
You have to starve them.
..

wrote in message
oups.com...
hello to all you heating gurus:

we have just moved into a new house, and the furnace was working fine.
for some reason, this afternoon when i went upstairs to put my son
down
for a nap, the thermostat said it was 74. it was hot. it was set at
62.
i turned it down all the way, and i still heard the furnace kick in.

is there any simple explanation to this before i call the plumber??

any help would be appreciated. the furnace is quite old, about 25
years, but our inspector told us that it was fine.

jae