Rheem Furnace Cycling ???
scottf...@smartt.com
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 isn’t working the way it
should.
The furnace is cycling and I don’t 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 don’t 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 don’t 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 ???
Thanks in advance,
Scott Farquharson
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Abby Normal
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.
sf...@my-deja.com
limit switch. Call your installer.
Scot
Sent via Deja.com http://www.deja.com/
Before you buy.
John Mills
>
> 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 ...
> 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 don’t 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 suspect drain trouble or possibly trapping in the flue pipe. The drain
hoses
on the RGRA are easy to kink if not installed properly. If the drain is
on
the left side of the furnace, the hoses need to be cut off at the proper
length so they enter the top of the trap with no kinking. A careless
installer
might not do this. If the drain exists right, make sure the hoses aren't
kinked
as they pass around the control box. Since the furnace runs such a short
time,
this is most likely the culprit but check to make sure there is no sag
in the
PVC flue. These have been reliable furnaces for us.
--
HVAC Advice, Pictures, Links
http://www.geocities.com/~johnmills
http://www.appelheat.com
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ICQ: 18370036
Eric Houkal
<a_bee_...@yahoo.spamoff.com> wrote:
>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.
>
>
>
There are also two drain hoses inside the furnace that have to be cut
to length (so that the drain outlet can be reversed Right/left) I have
seen these kinked on a couple of occasions, causing the pressure
switch to open. Other than that, it is possibly an airflow problem,
but that short a run time says probably not. On the other hand, that
long a run time makes it unlikely to be a board problem. I vote for
calling the guy who put it in- there is no reason for you to be
messing with this.
HVACMAN
airflow, and drains as has been suggested. Were the ducts sized by a
professional? Was the furnace installed by a professional? Although this doesn't
positively insure a correctly done job, you would likely be closer to it than
you are now...
Rfofaky
I had this same problem once with this same furnace, only a little bigger, and
the problem was a restriction in the furnace drain. It wasn't totally
restricted so the furnace was working erratically. I found it by hooking a
magnehilic gauge to the furnace and checking the pressure. Did you do this
furnace your self? If you didn't the contractor who did should be able to find
the problem and fix it. Another thing to look at, is to make sure the vent
piping is supported properly. If it isn't and there is any sagging, water could
form in the pipe and cause a pressure problem opening the pressure switch. I've
seen this happen before too.
scottf...@smartt.com
Thanks a million for taking the time and trouble to read and respond to my
call for assistance. It is very much appreciated.
This was a convoluted install. An acquaintance/friend of mine is a
plumber, has a gas ticket, worked in HVAC doing duct work a number of
years back, was working in another HVAC company earlier this year
installing 90% furnaces but not Rheems and even more recently (the summer)
was laid off and looking for some work. I didn’t feel confidant and didn’t
have either the knowledge nor tools for the duct work and while I felt
more confidant with installing the furnace, I thought it would be a good
idea to have somebody else who had actually done a furnace install to
oversee the whole exercise ... plus he needed some work. I asked him to do
the duct work and help with the install but he is a bit eccentric and has
some strong opinions. I ended up working with him on the install ... Now
he is working full time and it has been a bit of a trial to get him to
come and look at it.
Bingo (sort of) on the consensus solution from all. The condensate line
coming from the burner box (as opposed to the inducer fan) was kinked.
Unplugged the hoses and let them drain into a bucket while testing. While
it didn’t fully fix the problem, the furnace is now running for around 4
minutes. Noticed that shortly after the furnace shut off , I got a "rush"
of water from the furnace box condensate line ... hmmm ... connected the
hoses back to the left side mounted trap (just in case they were looking
for some back pressure) but the furnace still is shutting off after 4
mins. Note that the furnace is level left to right but leans backwards
about a quarter of an inch in total (not per foot). Comments ???
The PVC exhaust run is really straight forward (up 4 feet and out 2 feet).
The horizontal section is slightly uphill as required.
For the fun (my wife says this is not fun) of it, I put the blower to
medium high. Connected one side of a voltmeter to one side of the main
limit switch and the other side of the voltmeter to the side of the limit
switch. Reads 0vac. At around 4 mins into the cycle, the burners shut off
at the same time I get 24vac across the switch/sensor. Sounds like the
switch has opened and with my temperature probe on the top of the furnace
reading less than 120F, it seems to me to be a faulty limit switch.
Comments?
Anybody recommending NOT pulling the limit switch and placing my plastic
temperature probe inside and seeing what the sensor is reading ? Is this
inside the firebox, the primary or the secondary heat exchanger?
Anybody recommending NOT to fully pull the sensor, heat it (at the same
time with my temp probe) with a heat gun/hair dryer and see when it
trips???
Tried the same procedure with the drain pressure switch and it never moved
during the cycle. Guess it is draining okay now
Any other suggestions would be greatly appreciated
Thanks again,
Abby Normal
symptom was not mentioned in the original post.
Abby Normal
After the fan stops there is a big rush of condensate out of the furnace.
That is why the field installed VENT on the condensate line is specified to
be so high in the installation manual. If the furnace doesn't sit level then
it should slope towards the drain coming from the secondary heat exchanger.
Make sure the condenste line is vented, and that condensate is not getting
trapped in the line. My theory if the drain is more than 5 feet from
furnace, run a rigid drain line.
D.B.
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