Rheem RGLD won't ignite

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Old 12-27-07, 03:04 PM
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Rheem RGLD won't ignite

I have a Rheem RGLD gas furnace that is about 20 yrs old. The thermostat is calling for heat and I can hear both the gas valve open and the gas flowing however I'm not getting any spark. The blower isn't starting either although it turns on when switch the fan from "auto" to "on" on the thermostat. Anyone have any ideas?
 
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Old 12-27-07, 05:26 PM
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Originally Posted by detsirrom View Post
I have a Rheem RGLD gas furnace that is about 20 yrs old. The thermostat is calling for heat and I can hear both the gas valve open and the gas flowing however I'm not getting any spark.
You'll have to determine if spark is able to come from the control box. Because you could have bad control box, or bad spark plug wire, or bad gap at electrodes in the burner, or bad ground (tarnish or rust) between electrode and ground.

The blower isn't starting either...

It won't, without the burners going and generating heat inside the furnace, to build up the temperature inside the furnace, so a fan switch can come on at a preset temperature. Doubt that age furnace has fan timer (but could be wrong).
 
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Old 12-27-07, 07:27 PM
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Originally Posted by detsirrom View Post
I have a Rheem RGLD gas furnace that is about 20 yrs old. The thermostat is calling for heat and I can hear both the gas valve open and the gas flowing however I'm not getting any spark. The blower isn't starting either although it turns on when switch the fan from "auto" to "on" on the thermostat. Anyone have any ideas?

Unfortunately, I don't know offhand what kind of ignition system you have in that furnace. Is there a plastic box connected up with wires visible? If so, the name of the manufacturer and the model of the boc would be a help.


You really need to be able to understand the sequence of operation of the furnace and type of ignition system to diagnose the problem. You also probably need an AC voltmeter and an ability to understand the circuit diagram that's probably posted on the furnace. With that knolwedg, you can identify what how much of the furnace is working and at what point it's not working, which leads you to the likely problem(s).


You do some of that by pointing out what is working. But you don't provide enough information for me to advise you what would be worth to check next.



Perhaps someone else will have some ideas and suggestions.
 
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Old 12-27-07, 08:43 PM
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Originally Posted by SeattlePioneer View Post
Unfortunately, I don't know offhand what kind of ignition system you have in that furnace. Is there a plastic box connected up with wires visible? If so, the name of the manufacturer and the model of the boc would be a help.
My apologies for the lack of details. This is my first venture into HVAC repair and my first post.

My furnace has a Robertshaw SP715A Ignition Control.



Originally Posted by SeattlePioneer View Post
You really need to be able to understand the sequence of operation of the furnace and type of ignition system to diagnose the problem.
I did a search and found the following sequence for an SP715A on this thread http://forum.doityourself.com/showthread.php?t=119482

Step 1;
Thermostat contacts close calling for heat. Power is sent to the SP715A. The SP715A opens the first valve on the gas control supplying gas to the pilot, and energizes the high voltage spark at the same time.

Step 2:
The spark continues until the sensor circuit detects the rectified current through the pilot flame. If the pilot flame is not sensed the spark and pilot gas remain on for as long as there is a call for heat.

Step 3:
When the ignition control module senses the presence of the flame it energizes the second valve in the gas control. The SP715A continues to spark for a few seconds afer the 2nd valve opens to ensure stable operation.

Step 4:
The SP715A continuously monitors the pilot flame while the burners are in operation. If the pilot flame goes out, the SP715A will shut off the main burners, initate a spark, and attempt to relite the pilot.

Step 5:
When the thermostat is satisfied, power to the SP715a is dsicontinued and all burners shut down.

Originally Posted by SeattlePioneer View Post
You also probably need an AC voltmeter and an ability to understand the circuit diagram that's probably posted on the furnace. ...
My furnace doesn't have acircuit diagram anywhere and I can't find one online. I have an AC voltmeter and based on ecman51's recommendation tested for voltage at the ignition terminal on the control box by disconnecting the ignition wire and testing between the terminal and ground with zero volts when the thermostat calls for heat (I could hear the valve for the pilot light open at the correct time). Is this the correct way to test this? This leads me to believe that the fault is in the control box itself. I noticed that it grew warm although not hot when the thermostat called for heat.

Thanks
 
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Old 12-27-07, 09:24 PM
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Originally Posted by detsirrom View Post
I have a Rheem RGLD gas furnace that is about 20 yrs old. The thermostat is calling for heat and I can hear both the gas valve open and the gas flowing however I'm not getting any spark. The blower isn't starting either although it turns on when switch the fan from "auto" to "on" on the thermostat. Anyone have any ideas?
Ahhh. A picture, as they say, is worth a thousand words.


You have an intermittent pilot spark ignition system. Since you are hearing the gas valve open, you must have voltage to the ignition module. You can hear gas coming out ---- out the pilot light, I'm presuming, but no spark to light the pilot.


You should check the red/orange high voltage wire going to the pilot light to make sure it's connected. If I were diagnosing the problem, I'd disconnect the HV wire at the ignition module and ground a screwdriver and move the other end towards the HV connection of the ignition module to see if there is a high voltage spark present, which would indicate a defect in the HV lead or spark electrode.

If there is no spark, it's a pretty safe bet that you have a defective ignition module that needs to be replaced.


Another thing I would do would be to light the pilot with a match. Since it's probably just the ignition module spark circuit that's bad, the furnace will probably light and operate normally until the next time the thermostat is satisfied and shuts everything off. I can't really recommend you do that, as I suppose there is a certain risk that things might not go as I'd expect and you might not have the presence of mind to turn the power and gas off if something unexpected occurred.

You'd have to find an equivalent ignition module. You might not be able to find a direct replacement, and the universal substitutes like those sold by Honeywell might require some experience and judgment to install.

Also, it's pretty clear from the picture that this furnace is dirty and in need of maintenance work. Cleaning the pilot, burners, inspecting the heat exchangers, vent and chimney all probably need to be done.

It would probably be smart to hire a repair service to replace the part and do the needed maintenance work on the furnace.


You could shop around for a good price on replacing that "intermittent pilot spark ignition module" and getting the routine maintenance done on the furnace.
 
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Old 12-27-07, 11:07 PM
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I checked for spark as you recommended and there wasn't any so it looks like a bad ignition module. I'm not sure if I'm going to try it myself or not, but at least I have a better idea of what will be involved.

Thanks for the help. Have a happy and safe new year!
 
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Old 12-28-07, 03:26 PM
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Fixed

I replaced the ignition module with a Uniline 780-715 today and it's working perfectly.

Thanks for your help Pioneer.
 
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