Rheem Natural Gas Furnace - somtimes lights, sometimes not.

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Old 04-11-10, 09:43 AM
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Rheem Natural Gas Furnace - somtimes lights, sometimes not.

Just had the repairman replace the Robert Shaw control box for this about 2 mons ago. I thought all the problems were solved. However, about 1 month ago it started acting like it's old self once again which is that the main burner won't light and sometimes the pilot won't light, then the furnace gives up and turns off. Leaving us in the cold. This was the same exact problem I called the repair service for. He diagnosed the old box as having a broken circuit board. Could it be possible the brand new control box is defective also? This thing is driving me crazy................
 
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Old 04-11-10, 05:43 PM
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Pilot won't light

Since the furnace does not have a pilot which stays lit all the time, I presume there is an exhaust blower. Does this exhaust blower run when there is a call for heat? All furnaces with exhaust blowers have to prove draft before ignition. Can you see or hear any sparking at the pilot burner?
 
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Old 04-11-10, 07:03 PM
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Hi Grady.
The exhaust blower comes on fine when there is a call for heat. The pilot lights too but...............sometimes it won't, and when it doesn't light there is no clicking, sparking sound. When this happens, the fan just runs until it finally gives up and turns the whole unit off. I've been reading some posts here and today I fiddled with the fan limit switch a little. It's suppose to turn on at 130 and off at 90. I adjusted it to these settings after seeing it was set for about 120 and 80 respectively. Now the fan comes on like it used to years ago which is to say after the main burner goes out and the fan stops, there is a lull of a few minutes then just the fan comes back on to use the residual heat from the still hot burners. Since this is the way it worked brand new, I assume this is the way it's suppose to work.
 
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Old 04-12-10, 07:12 AM
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Well, I thought maybe it was fixed but woke up to a cold house again this morning. The problem is the same as before the repairman replaced the control box which is the pilot lights but the main burners don't then the whole thing shuts off. I think I will give the service company another call today.
 
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Old 04-12-10, 08:47 AM
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The reason there is sometimes no sparking/clicking is that it may have tried several times, and then locked out the ignition control.

I made a real long detailed post on what to look for last night, but it erased, so I quit in a huff. I will now to be more succinct, especially hearing you are likely going to call someone out.

If I was you, and say knew how to use a voltmeter, I would make certain tests to see if the pilot wire to the gas valve got signal, and that voltages were not eratic, which if so can indicate a bad module. But if steady volts, until it goes away in seconds, this likely is not the module, but can be caused by -

Ignitor current being bled away elsewhere. If no spark, get the spark wire away from any metal it may be resting on, and inspect the wire to see if discolored there.

Or the flame sense ground path is poor due to oxidation on any metal part the pilot flame comes in contact with. The pilot flame makes micro voltage and takes a path back to the ignition module. If it cannot do that, the ignition process quits at that point.

Or a poor "burner ground" wire. Often these get very corroded where connected onto the pilot assembly.

Or a partially plugged pilot orifice. (The assembly can be removed and the pilot reamed out so that more pilot size and temp can make pilot flame for flame sensing.)

Make sure any pin or spade connector is not loose on the igniton module. What I simply do is remove, then reattach again.
These can all be DIY checked out.
 
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Old 04-13-10, 08:26 PM
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Thanks ecman51,
Originally Posted by ecman51` View Post
Ignitor current being bled away elsewhere. If no spark, get the spark wire away from any metal it may be resting on, and inspect the wire to see if discolored there.
Did this and everything looks good. No discoloration or fraying.
Originally Posted by ecman51` View Post
Or the flame sense ground path is poor due to oxidation on any metal part the pilot flame comes in contact with. The pilot flame makes micro voltage and takes a path back to the ignition module. If it cannot do that, the ignition process quits at that point.
Took the pilot and sparker assembly out today and inspected it. Cleaned the sparker tip with emery cloth then brush the whole thing with a small wire brush. Then blew the pilot tube out with my air hose and also the pilot gas tube.
Originally Posted by ecman51` View Post
Or a poor "burner ground" wire. Often these get very corroded where connected onto the pilot assembly.
The wire looks brand new.
Originally Posted by ecman51` View Post
Or a partially plugged pilot orifice. (The assembly can be removed and the pilot reamed out so that more pilot size and temp can make pilot flame for flame sensing.)
Blew it out with my airhose. No blockage.
Originally Posted by ecman51` View Post
Make sure any pin or spade connector is not loose on the igniton module. What I simply do is remove, then reattach again.
These can all be DIY checked out.
All connectors are secure.

One thing I did notice today was that my entire pilot assembly was floating in mid-air! The only thing holding it was the small pilot gas line. So I secured it against the frame very securely in case it needs to be grounded. When I put everything back together, it fired right up. Then tonight when it got cooler and we needed it, it fired up but then shut off!! I watched this closely for about 5 rounds when I noticed the fan limit switch doesn't really move smoothly. It moves a little jerky. I'm thinking maybe the fan limit switch is getting stuck at the off position and causing it not to light? The reason I'm leaning towards this scenario is because when I move things around and lightly tap on things, it will fire up, possibly because I happened to knock the limit switch out of a stuck position? Could a sticky limit switch cause this? Thanks!
 
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Old 04-14-10, 08:34 AM
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See if rapping on that sharply, without causign too much vibration throughout the furnace, is what fixes it everytime.

What is odd though about this is that you never said you were having a problem with your furnace high limiting and shutting off on you after it has been running a while.

A furnace just does not up and high limit out in seconds after ignition. It takes longer. So if it did not high limit - what could make the furnace trip out the high limit, so that it gets stuck there?

Not unless - during the preceding run, when the furnace DID run, that it limited then, and you mistakenly thought the furnace shut off due to the stat temp being met. And then stayed stuck there. Simply highlimiting a Honeywell will not prevent the next cycle from occuring, if it limited, but then the dial rotated to the cooler position after it was off, as normally happens.

On furnaces with these Honeywell fan-limit switches, I believe from my recollection with some of the various brand furnaces that we have, that have one in it - that they do not shut off the furnace and lock it out with the blower running - as furnaces do that have 24 volt safety circuit limit switches.

What happens is the fire shuts off say in a few minutes where then it finally high limits(if a person has such an issue), and then the blower continues to run - and when the exchanger cools down, it will let the furnace fire back up again.

If, when you rap on the fan-limit switch, you are causing vibration in the entire furnace, it could be any connection point that is causing the furnace to come back on, including a bad connection, bad jack, or relay on the board, or even if the pressure switch were marginal(which can have various causes besides the switch being bad).

Also. Observe the dial on the fan-timer, to see when the furnace does run, if you see it rotate over to the limit position, which is usally set about 180-200 on these things. often the behavior is that it climbs toward that limit mark, then suddenly snaps to that postition, and then the flame goes out. See if that happens or not, so we know if we have to pursue other areas.
 
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Old 04-14-10, 09:12 AM
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Originally Posted by ecman51` View Post
See if rapping on that sharply, without causing too much vibration throughout the furnace, is what fixes it every time.
I haven't done this every time but I CAN tell you it fixed it when I tapped on it this morning.
Originally Posted by ecman51` View Post
A furnace just does not up and high limit out in seconds after ignition. It takes longer. So if it did not high limit - what could make the furnace trip out the high limit, so that it gets stuck there?
I'm thinking it gets stuck in the "off" position. Not the "high limit" position.
Originally Posted by ecman51` View Post
Also. Observe the dial on the fan-timer, to see when the furnace does run, if you see it rotate over to the limit position, which is usally set about 180-200 on these things. often the behavior is that it climbs toward that limit mark, then suddenly snaps to that postition, and then the flame goes out. See if that happens or not, so we know if we have to pursue other areas.
Ok, Will do this today. I think I am also going to take the switch completely out today and clean it and have a good look-see at just how smooth or rough it operates. Thanks again!
 
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Old 04-14-10, 12:42 PM
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Originally Posted by ecman51` View Post
Also. Observe the dial on the fan-timer, to see when the furnace does run, if you see it rotate over to the limit position, which is usally set about 180-200 on these things. often the behavior is that it climbs toward that limit mark, then suddenly snaps to that postition, and then the flame goes out. See if that happens or not, so we know if we have to pursue other areas.
Ok.....Just got through pulling out the Honeywell fan limit switch and gave it a look over and blew it out with my airhose. It had some dust on the coil in the probe but other than that, looked to be in good working order. I reinstalled it and watched it as the furnace cycled. Furnace fan goes on at 120 and off at 90. However after the stat was satisfied and stopped the main burners, I watched the limit switch. It got stuck at 120 so I barely touched it with my finger and it switched on the fan to use the residual heat to cool off to 90.
 
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Old 04-14-10, 05:20 PM
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So after the stat was satisfied and the flame went out and the blower continued to run, it came down to 120, and the blower shut off?(which it should not) -at 120?, not 90? - until you rapped on it and the blower came on again?
 
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Old 04-14-10, 05:34 PM
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Originally Posted by ecman51` View Post
So after the stat was satisfied and the flame went out and the blower continued to run, it came down to 120, and the blower shut off?
No. The blower continued to run with main burners out until the limit switch reached 90.

Originally Posted by ecman51` View Post
....until you rapped on it and the blower came on again?
I tapped the limit switch dial after it had cooled down to 90 with the blower off, then residual heat raised the temp up to 120 and this is where the limit switch got stuck. It should go on at 120 to cool the exchanger off to 90 again but it didn't until I tapped the limit switch wheel. After I tapped it the blower came on again without the burners to cool it off to 90.
Thanks!
 
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Old 04-14-10, 06:30 PM
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Sounds like you need a new switch, if rapping on it gets the dial to go to (very) different positions.
 
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Old 04-14-10, 07:45 PM
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I have a Honeywell 4064"A" limit switch. All I can find online are 4064"B" units. Does anyone know what the difference between an "A" and a "B" model is?
Thanks!
 
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Old 04-14-10, 07:48 PM
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Originally Posted by ecman51` View Post
Sounds like you need a new switch, if rapping on it gets the dial to go to (very) different positions.
It really doesn't go to different positions, it just gets hung up on it's way to the correct position.
Thanks!
 
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Old 04-14-10, 08:01 PM
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L4064

I couldn't find any "A" models on Honeywell's site. I suspect it has been superseded by the "B".
 
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Old 04-14-10, 09:52 PM
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Originally Posted by Grady View Post
I couldn't find any "A" models on Honeywell's site. I suspect it has been superseded by the "B".
Thanks Grady......
Tonight I have a new problem...... The main burners came on, everything looked normal, then the blower went off and left the burners burning! It went to the high limit of 150 and shut down then reignited after it cooled down to 120 then went through a normal cycle from there. Needless to say.........GI2
Thanks!
 
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Old 04-15-10, 08:23 AM
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I think we already know that your fan-limit switch is screwy. Maybe from rapping on it, it is falling apart inside or arced contacts or something, or the fan wire is real lose now - and now losing connection.
 
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Old 04-15-10, 07:45 PM
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Fan/limit

I agree with ecman. I too think the fan/limit has had it. Time for a fresh one. You will need to know the insertion depth before ordering.
 
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