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QUESTION:In September, I replaced my furnace. Out went the old 60K BTU (input) <60%
furnace as well as the virtually useless duct system (the whole thing). In
went a new Rheem Classic 90 Plus 45K BTU (input) 94% Model RGRA04EMAEB
furnace as well as an entire new duct system. Of course, the system was
basically OFF since installation but now that the colder weather has set
in ...
It is taking forever to bring the heat up in the morning. During the day,
the thermostat is set to 72F. At night, the setback is to 66F. In the
morning, the outside temperature is about 36F. At 6:30am the thermostat
goes to the daytime setting of 72F.
Three (yes 3) hours later and the temperature in the house has risen to
68F. With the old furnace, the temperature was at 72F in less than an hour
and half AND that is before I replaced the furnace, ducting, insulated the
main floor walls, insulated the basement floor walls and replaced all the
leaky windows with new double glazed. Something isnt working the way it
should.
The furnace is cycling and I dont know if it is designed this way or if
the furnace is temperature limiting itself or doing something else. Here
is what is happening ...
The whole firing process goes according to the troubleshooting charts
(pre-purge, igniter, burners on, blower on) and everything is hot and
wonderful ... then the part I dont understand ... the burners just shut
off 2 to 3 minutes after burn start. Note that the thermostat is still
calling for heat (I have even bypassed the thermostat) AND that the flame
sensor LED on the control board was "good" up until the time the burners
shut off. The blower continues to run until the blower shutoff time has
elapsed but immediately after the blower shuts off, the firing sequence
starts again.
I opened a small hole in the plenum and measured the temperature about 8"
above the top of the furnace outlet. Not the fastest reacting thermometer
in the world, however, but here is what I measured today:
- with the blower set at medium low, the burners ran for 2min 12secs with
the temperature reaching 117F
- with the blower set at medium high, the burners ran for 2min 36secs with
the temperature reaching 114F
Here is what I measured last night
- with the blower set at medium low, the burners ran for 2min 50 secs with
the temperature reaching 122F
- with the blower set at medium high, the burners ran for 2min 45secs with
the temperature reaching 118F
The furnace name plate indicates a rise of 30F to 60F (okay here) with a
limit setting of 140F
I dont believe the furnace should be cycling on or off. Do I have a
possible faulty limit sensor (any suggestions on how to check) or do you
have any suggestions on what ELSE could be wrong ?
ANSWER: Scott if it wasn't for the fact that you said you jumped your thermostat, I
would have guessed that your heat anticipator setting was way low.
Make sure that the furnace is draining properly, if the condensate line is a
long run of flexible tube, the condensate can trap itself over and over
again. If the furnace has problems draining, there is a pressure switch
which will open.
Other than that, I can only guess that it is the board. Call the guy who put
it in, you are under warranty.
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