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paul murphy 11-25-2007 11:35 PM

Ruud 80 plus unit, itermittently no heat
I have a 1989 ruud 80 plus unit, model # UGDE-14 ERAJS upflow furnace.
I have an intermittent problem. The thermostat calls for heat, the
pre-purge sequence starts, the draft inducer does not turn on / the glow
stick does not turn on, the systems shuts down......I reset the
system, the furnace will fire, but this reset does not work 100% of the time. I replaced the glow stick, and am seeing if this makes a difference. (I don't think it should as the the glow stick would turn on intermittently. It seems the draft inducer is not receiving a signal???????????

I have had two HVAC guys look at this (one on Sunday :furious: ) to no avail......

#CARRIERMAN 11-26-2007 11:53 AM

Hi paul murphy

The problem you are having with your furnace is caused by one of two problems with this particular furnace. The most common is the vestibule limit gets corrosion built up in it. This limit should be black in color, it will be mounted about midway into the front of the furnace it is approx. 2"x3.5" rectangular in shape. It will have two wires on it that are typically red or orange. All you will have to do to verify this is the problem, when the furnace fails to light jump the two wires together and see if the furnace fires up. If it does, replace the limit and you shoud be fine. The other problem this furnace has had is the control board. This furnace should have a control board that has two diagnostic lights on it. If you are lucky you already have the upgraded furnace with the three diagnostic light board. If you have the two light set up you can purchase an upgrade kit for about $200.00 dollars. If you already have the three light set up, just replace it with the same board. Those are the most common problems with this furnace.

Good luck

paul murphy 11-26-2007 02:55 PM

thank you Rusty...

ycl1688 12-06-2007 12:58 PM

i have the same model # furnace. have the igniter replaced feb and nov
this year, what gives ?

spent quite a bit on emergency calls.

what is the igniter that fits this furnace, so that i can replace it next
time it quit on me ? how easy it is to replace?

paul murphy 12-06-2007 10:23 PM


Originally Posted by ycl1688 (Post 78761)
i have the same model # furnace. have the igniter replaced feb and nov
this year, what gives ?

spent quite a bit on emergency calls.

what is the igniter that fits this furnace, so that i can replace it next
time it quit on me ? how easy it is to replace?

ycl - my probem actually turned out to be my thermostat. the previous owners of my house cheaped out and didn't want to line the chimney to vent the they got a jerlyn (sp?) fan which acts as a booster to exhaust the furnace out the side of the house instead of the chimeny (which is one foot away from the furnace) it works like this - the thermostat sends a signal to the booster fan which triggers the heat exchanger in the booster fan to send a signal to the furnace to light up. in my case, the heat exchanger on the booster fan was not always getting the thermostat signal. i replaced the thermostat and have not had a problem since.

may or may not be your situation, but the thermostat is only a 30.00 investment---good luck

brianteel 01-03-2008 11:39 PM

My heater is doing basically the same thing. i can see that the vent fan is coming on when it is cycling but shuts right off. after about 2 minutes the whole thing shuts down. I have had a guy out a few times now and it works every time he comes out. I am trying to figure out if i should start with the thermostat and just keep changing parts or is there some place else i should be looking first

paul murphy 01-06-2008 07:00 PM

It is frustrasting, the problem in my furnace would never occur when i had HVAC guys over either.

In case your ceramic glow stick (Furnace Igniter) does not come on (and it sounds unlikely because you said it does not occur when the hvac guys are there which makes the problem seem intermittent) and you have the same model # furnace I do (listed below) , the glow stick maker is Robert Shaw part # 41-408 (Hot Surface Furnace Igniter) It is easy to replace.

If your stick does work, in my opinion, the easiest (and probably cheapest) way to start is the thermostat. I bought a programmable Hunter model from Home Depot for 30.00. I replaced it 1 1/2 months ago and have not had a problem since.

Basically, $30.00 will rule the thermostat in or out of the equation. After the thermostat, the next place my hvac guy told me to look was to replace the entire Printed Circuit board inside the furnace. I would have felt more comfortable doing this if the new board was a drop in replacment, but there was rewiring involved which I would not risk doing myself.

good luck

brianteel 01-06-2008 08:13 PM

i did the thermostat now. i do know that when i turn the furnace off and on the vent fan is not turning on sometimes that causes it to shut off. i have a feeling that it might be the circuit bored but i really have no idea

bigMikeB 01-06-2008 10:24 PM

Change the furnace it's cheaper than changing one part at a guess, I mean time.

paul murphy 01-06-2008 10:27 PM


you didn't say, is your igniter (glow stick) turning on?

read Rusty's reply to my original post.....hopefully it will help you out.

bigMikeB 01-06-2008 10:29 PM

Buying and using a meter will help out more than guessing or assuming anyday.

paul murphy 01-06-2008 10:35 PM

all due respect mike, had I listened to the second HVAC guy that tried to fix my problem, I would have bought a new furnace because of a bad thermostat.

brianteel 01-06-2008 11:57 PM

the ignitor is new so is the stat

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