Furnace heat cycle

[Puddin' Man]

Little bungalow in US midwest. Heil gas furnace on it's 3rd season. Standard forced air, std install. Gen'lly works well.

heat cycle:

1.) tstat calls for heat 2.) inducer fan spins 3.) igniter element (like glow plug) heats up 4.) after about 20 sec. for 1.) and 2.), gas valve opens, burners fire 5.) safety: if heat sensor stays cold, gas valve closes.

Works OK about 2 of 3 times.

The third time, works OK thru 3.), I get a click like when the gas valve opens, but the burners don't fire. Then it goes back thru the cycle and works.

The igniter always heats, I can see it glowing.

Igniter's not getting hot enough? Other ideas??

Thx, P

"Take Yo' Hand Out My Pocket (I Ain't Got Nothing What Belongs To You)!" - Rice Miller, who probably never even _heard_ of GW Bush, Paulson, etc

[Puddin' Man]

If you're talking about the heat sensor in 5.), I don't understand.

The inducer runs it's little cycle, the igniter glows. It *sounds* like the gas valve opens, but the burners don't fire.

You're saying maybe the heat sensor has crud from previous cycles and shuts the gas valve down before the burners have a chance to fire???

The burners don't fire and then shut down prematurely. They fail to fire at all.

P

"Take Yo' Hand Out My Pocket (I Ain't Got Nothing What Belongs To You)!" - Rice Miller, who probably never even _heard_ of GW Bush, Paulson, etc

[Tony Hwang]

Common problem. Clean the flame sensor with emery cloth. When flame comes on sensor generates very small amount of current which is sensed by control board logic.

[Rich]

I wish I had this in my back pocket 3 weeks ago when I had to call in a Sunday tech to do the exact same thing for $110 instead of me doing it, for a lot less!

Thanks for the great advice, Rich

[Pete C.]

The gas valve may be sticking, making a clunk, but not actually opening.

[Tony Hwang]

When inducer motor comes upto speed pressure switch should trigger next is ignitor coming on(if it's not spark type, it should glow bright) then valve opens, gas ignites, flame sensed, blower comes on. What model furnace? No trouble code?

[Puddin' Man]

I refrain from relating additional info to Mr. Tony as there is evidence that it might further confuse him. :-)

P

"Take Yo' Hand Out My Pocket (I Ain't Got Nothing What Belongs To You)!" - Rice Miller, who probably never even _heard_ of GW Bush, Paulson, etc

[Claude Hopper]

Take the safety stuff off, go outside and throw it as far as you can.

[Stormin Mormon]

If the inducer was the problem, it should not get to the igniter stage. I'm wondering if the igniter isn't drawing enough amps to satisfy the board.