Robertshaw Ignition Problems

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  #1  
Old 10-06-04, 09:15 AM
ACE&D
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Unhappy Robertshaw Ignition Problems

Hi, can someone help me out. I have a Robertshaw furnace that won't light.

Here's what I do know...

I have spark from the ignition to the pilot light nozzle but the pilot light won't ignite.

The exhaust fan is running

The ignition sequence continues to throw and arc repeatedly eventually timing out.

The gas is ON, the valve on the gas regulator is ON but still no ignition flame.

It's a Robertshaw 7100DER series gas valve and "S" series pilot. I did clean the end of the ignitor and have visually confirmed it has spark.

Any suggestions?
 

Last edited by ACE&D; 10-06-04 at 10:17 AM. Reason: more detail...
  #2  
Old 10-06-04, 12:41 PM
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Check to see that when it's calling for heat (i.e., when the inducer fan is running and the control is sending the spark) that you have 24VAC across the common (MV/PV) and PV terminals of the ignition control module. If you do, and if you are sure there is sufficient gas pressure going to the gas valve and that the pilot orifice is properly situated relative to the spark, you may have either a broken wire connection or a bad gas valve. You said this control locks out after trying to light the piolt. Is your furnace propane? If so, are you sure you have gas?
 
  #3  
Old 10-07-04, 09:51 AM
ACE&D
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Measured Voltage

I measured the voltage between the MV/PV, PV terminals and didn't receive any reading. What does this mean?
 
  #4  
Old 10-07-04, 09:56 AM
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If while the unit is sparking (which means you are getting 24V to the ignition control) you are not getting 24V across the MV/PV and PV terminals there is either a bad wire or connection, or the ignition control itself has gone south.
 
  #5  
Old 10-07-04, 10:00 AM
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To clarify, my response refers to the MV/PV and PV terminals on the control module, not the gas valve. If (while sparking) you get 24V across these terminals on the module but not across the C and P terminals of the gas valve, there is fauly wiring between the module and the valve. If you are getting 24V across the C and P terminals of the gas valve but no gas is coming out of the pilot orifice, the gas valve is bad.
 
  #6  
Old 10-08-04, 06:05 AM
ACE&D
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Okay, thanks for the help. I measured both and I wasn't getting a reading at all from either the MV/PV terminals or the C/P terminals on the gas regulator. Still no gas. So I'll work on replacing the ignition control.

Thank you for your help. You've saved me a lot of money.
 
  #7  
Old 10-08-04, 06:56 AM
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Make sure you have checked everything thoroughly before you buy another ignition control. It seems to me that failure of the ignition control to supply 24V across the MV/PV and PV terminals when sparking would be an unusual failure. What type of control module do you have?
 
  #8  
Old 10-11-04, 10:08 AM
ACE&D
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I have a Robertshaw Ignition Control. I had a buddy come over and we called for heat and then checked again on the gas regulator. I had 24V across the Pilot terminal (P), but nothing across the Main (M). Upon his expertise we bridge the two and gas started flowing but not out of the pilot light, only out of the main valve. We quickly shut it down.

Interestingly enough I got a quote from the dealer for a new ignition control for $ 169.00. I then called a parts dealer and he quoted me the same ignition control for $ 85.00.

I'm holding out on replacing it (we had a warm weekend). The furnace is 18 years old. Perhaps its time for a replacement, some rust and mineral build up on my heat exchangers and these continuing problems lead me to believe the $ 600 investment might be a good idea.

Your thoughts? Thank you again for your expertise.
 
  #9  
Old 10-11-04, 01:07 PM
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Before relegating the gas valve to the trash can, check the pilot orifice and line for obstructions (spiders love to nest in these) that might be preventing gas flow. If the line and orifice are clear, the gas valve is probably bad. Also, deliberately energizing the main valve in the absence of a means to ignite the gas (by jumping the pilot solenoid voltage to the main valve solenoid voltage, as you described) is not recommended.
 
  #10  
Old 11-28-10, 06:07 PM
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I have a robertshaw ignition control module 780-910......when my heater calls for heat everything works and the furnace comes on but after a couple of second it go out....my control module indicator light flashes one time every couple of second.........can someone tell me what that means? and how do I fix it?
 
  #11  
Old 11-28-10, 07:08 PM
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Please don't revive old threads. It rapidly becomes confusing for those trying to help you. Repost on a new thread.
 
  #12  
Old 11-29-10, 06:31 AM
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Wow. This is an old thread. Suggest that you clean the flame sensing rod with fine steel wool.
 
 

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