Author Topic: Ignition Failure  (Read 4782 times)

Offline DarrellT

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Ignition Failure
« on: December 27, 2007, 04:58:04 AM »
  I need help or pointers to solve this issue with my aunt's furnace (Honeywell with SV9500 Smartvalve). Over the summer she had it repaired. The transformer had went out. The guy put in a 10VA transformer in. I have now changed that to a 40VA transformer as reccomended. The cycle seems to start right. Call for heat comes, the inducer motor turns on, the pressure switch closes, the igniter glows, pilot gas comes out. But it dont light. I can manually light it at this point. I have already put a new igniter/flame rod assembly in the unit. Even after manually lighting it nothing else happens. I am not understanding how the flame sense makes a circuit with one wire? I am also not understanding why I can manually light the gas, and the igniter (glowing orange) won't. I have read in this manual (http://www.transtaracsupply.com/pdf/sv95control.pdf) that the pilot gas tubing acts as the ground for the flame sense/ignighter assembly. But I don't see how the circuit is made. Any help towards a solution is apprieciated.

Darrell T

Offline TECH X

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Re: Ignition Failure
« Reply #1 on: December 28, 2007, 01:23:00 PM »
The sequence sounds right.  As soon as the igniter is energized, the pilot gas should be leaving the gas valve.  If the igniter is not lighting the pilot you could have a dirty pilot or poor gas pressure.  Are you certain there is gas every time the igniter glows?  It wouldn't be uncommon to have a bad smart valve.  I have seen a bad valve energize the igniter but not the gas valve.  It's also very common with that valve to get a pilot but no main burner.  Double check you are in fact getting 24V from the gas valve, under load.  Leave the igniter plugged in and measure voltage across the 2 blue wires.

The 2 blue wires energize the igniter, 24V and Common wire.  The black wire is the flame rod wire.  The heat from the pilot creates a micro amperage down that wire to the gas valve.  I have a special adapter to measure flame signal, you could just cut the black wire and measure in series with a multi meter that can measure micro amperage.  Use a maret to attach the wire back together.  There is no need to clean this flame rod, as it sheds its skin automatically.  I have seen people change the igniter and leave the flame rod touching the pilot hood that will cause the burners to cycle off after they have lit.

The older smart valves have a brown on/off dial.  The new valves have a black on/off switch.  Sometimes moving the molex connector on the valve itself will get it to start working again.

Honestly I have never seen the igniter energize and not light the pilot if there is gas.  If you’re lighting it manually then obviously there is gas.  The red hot igniter should be lighting it.  I'm curious to know what's preventing the pilot from lighting. 

Sounds to me like a bad smart valve.

Offline DarrellT

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Re: Ignition Failure
« Reply #2 on: December 28, 2007, 10:52:17 PM »
 I had the flame sensor touching the ground shield. Once I bent it back a little the sequence works fine if I manually light the pilot. I Power up, call for heat comes, inducer motor on, pressure switch closes, igniter starts to glow orange with 22.5 volts which then ramps slowly to 23.4 volts, pilot gas is flowing, nothing happens, I then light the pilot by hand, the pilot runs a second, the igniter stops glowing, the main burner gas turns on and lights from pilot flame, once to temp it shuts down. Have you ever seen an igniter not hot enough to light the gas? Thoughts?

Offline HVACJOE

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Re: Ignition Failure
« Reply #3 on: February 24, 2008, 10:05:29 AM »
Just a quick question, the HSI you got (that glows) is it a thin piece shaped like a u, or is it more like a post about 3/4 of an inch high that tapers down a bit at the top, if it is the second one, its a generic replacement that does not seem to reach necessary ignition temperature, I had to get our local wholesaler to stop selling them and bring back the oem ones.

Offline TECH X

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Re: Ignition Failure
« Reply #4 on: February 24, 2008, 02:39:39 PM »
That's interesting.  I just ran into this problem.  I noticed the original 24V igniter was only glowing red at the top and not the bottom.  I figured it was the igniter as well, but replaced it with the round tapered replacement your talking about.  It did the same thing.  The pilot gas was just being sucked into the burner ports by the ventor motor without lighting.  I then put on ICP replacement igniter and it worked fine.

Offline ProTemp

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Re: Ignition Failure
« Reply #5 on: February 27, 2008, 02:58:59 PM »
Try an ohms test and then see what the amp draw is on the hsi...This will tell you is you are getting hot enough for ignition. Also check pilot pressure and pilot position to hsi. Ive seen pilot gas being drawn away from the hsi cause the ventor restrictor disk is missing from its housing. Depending on the model of furnace you have also check the heat exchanger for possible holes or even bad rivets.