Heil furnace continuous fan, no heat, ignition problem?

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Old 02-06-11, 01:10 PM
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Heil furnace continuous fan, no heat, ignition problem?

Have a Heil hot surface ignition gas furnace which first presented continuous fan no heat. After shutdown and kinetic repair of fan limit timing switch it started back up.
Became progressively unreliable and now wont heat. Blowers turn on, hot surface igniter turns on and there is a brief 25 volt surge to gas control valve but not flame.
Any one know how long the current is supposed to stay on a gas control valve?
 
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Old 02-06-11, 01:42 PM
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describe brief 25 volt surge in seconds. it should stay on for at least 10 seconds give or take to allow for all burners to ignite and then flame signal to be produced. viewing through the window in the blower door can you see a diagnostic code flashed by an LED?
 
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Old 02-06-11, 02:31 PM
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You need to describe in detail the sequence of events that happen when the thermostat is turned up.

Unfortunately your initial post is a hodge podge of things happening and is of little help.
 
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Old 02-06-11, 02:50 PM
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chain of events

Will try to make it clearer. When thermostat makes a call for heat, the blower (in the same compartment as the burners) starts to blow. Shortly after that the hot surface igniter starts to glow. Igniter stays lit for about 5 seconds. When unit is functioning the burners lite towards the end of HSI burn. Shortly after that, the lower fan/blower starts to distribute heat through the house. Currently the fans, blowers and HSI all cycle but the burners do not light. After while, and repeatedly thereafter, the hot surface igniter will glow for awhile as if trying to light the burner, but there is no flame and unheated air flow through house continues nonstop. There are two black wires from ignition controller to gas control valve.

The controller puts out a 25 volt current for only a second or two while HSI glows. Originally thought it was a faulty gas control valve and replaced it five days ago. The System worked for about three days, started intermittently for two days and now will not fire up at all. It is an older Heil unit, partial mod number NULK 125 and the rest is missing. The fan limit switch is a Camstat Henry 7 inch f560 and the ignition controller a Rogers White 50E47-150 and no led lights to assist in diagnosis. There is no wiring schematic. Can post pictures of any of unit parts. Thanks for the help.
 

Last edited by mjohnsn; 02-06-11 at 03:08 PM.
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Old 02-06-11, 03:24 PM
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If I'm understanding you correctly, the HSI heats up normally.

After 30 seconds or so to heat the HSI, you should have 24 VAC being switched on to energize the gas valve and turn on the main burner gas, which should light promptly off the HSI.

The control module will typically leave the main burner gas on for only thyree seconds or so if the main burners don't light.

I take it that the main burners aren't lighting? Check to be sure you have gas to the furnace --- the valves must be on, the gas valve must be turned to the on position and you need to have 24 VAC to energize the gas valve.
 
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Old 02-06-11, 04:59 PM
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Gas control manual switch is on. Cut off valve to unit is open. Propane tank is filled to top. Gas control valve is new unit. HSI heats up normally. Controller throws 24 VAC to energize gas valve while HSI is glowing but only for a second, two at the most. Unit has fired up once in last 24 hours but did not stay lit. After lighting I went upstairs. About 20 minutes later noticed it was blowing cold air again.
 
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Old 02-06-11, 06:53 PM
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If you are getting 1-2 seconds of power to the electric gas valve, you should be getting gas from it for the main burners, even if only briefly.

I'd open up the gas fuel line at the furnace union or flex connector to verify that you have good gas pressure.

Typically the gas will be turned on for about three seconds to give the main burners a chance to light. One second isn;t long enough. Two is marginal.

I take it NO gas comes out of the burners during this trial for ignition? Often you can hear or smell the gas being released, but check to be sure.
 
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Old 02-06-11, 09:04 PM
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Gas pressure appears to be good. Range runs off the same line and burners are at full power.
Can not hear or smell gas when gas valve is energized. Now notice that igniter only cycles twice. Exhaust fan stops but house blowers continue.
 
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Old 02-06-11, 09:09 PM
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sounds like a control board may be faulty or you are having an issue with a pressure switch dropping out while trying to ignite
 
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Old 02-06-11, 09:46 PM
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Whoa!!!!! you said propane!!!!

Did you buy the LP conversion kit for the new gas valve? They are sold as Nat gas valves. Measure the gas pressure. It should be a typical 10.5""WC... where as nat is only 3.5"WC and the springs and spuds are different... Be careful...an old addage......." Go gas, go boom!"
 
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Old 02-07-11, 12:44 AM
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I agree with HVAC that you need some tests to verify that the correct voltage to the ignition module is being maintained.

And I agree that the gas pressure should be verified while the furnace is operating ---- checking to be sure those range burners are staying at full power which the furnace is operating would confirm that.

But I don't have confidence in Johnson being able to check things with enough initiative and accuracy to identify what's happening.

It could well be a bad module, but it could be other things as well. I don't see enough diagnostic skill on Johnson's part to identify the cause at this point.

It takes a measure of skill and understanding to identify the real cause in a case like this. I don't see that happening over the internet, but perhaps I'll be surprised.
 
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Old 02-07-11, 03:41 PM
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Final Call

FYI. LP conversion kit was included in install. Gas line pressure was not the problem.

Hvactechfw nailed it. Replaced controller and everything toasty again.

Thanks to all.
 
 

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