furnace will not fire

[trbomax]

The lp distributer came this morning and tested all my new lines,filled the tank,purged everything.When we tried to fire the new goodman 96% we get nothing. Combustion air blower comes on,igniter lites up, but no gas flow. Checked for 24v at the valve and nothing. Checked for power at the air pressure switch,nothing. The transformer is supplying 24v to the board . The guy who did the lp test and sign off said "I guess your on your own from here"! Am I missing anything or is it time to call in professional help?

 

[phbsales]

Look at your sequence of operation. Combustion blower starts allowing the pressure switch to close, allowing the ignitor to glow. Final steps are gas valve opens and flame is proved.

You either have a bad gas valve, or gas pressure is not set properly.

 

[rickairmedic]

Ok you have no power at the air proving switch . This means that one of the safety switches is tripped . Look in the burner area and follow the wires from the gas valve . One of the wires will go straight back to the control board the other will go to a safety ( round disc with 2 wires going to it . ) There is a small button ontop of the disc between the wires . Push the button down and continue to follow wires and check all the other safeties along the way back to the control board . There should be one on the squirrel cage ( Main Blower assembly ) as well which isnt easy to spot . Try this and see what happens and let us know .


There is also an LED light on the control board that will flash a code and on the blower compartment door there is a list of these codes .


Rick

 

[phbsales]

Just a point, Rick. If the ignitor glows, the pressure switch is closed. If the OP was using a meter and reading across the terminals, he's going to see zero voltage, because he's reading across the line.

All the safeties are closed. The gas valve does not seem to be opening.

 

[rickairmedic]

Just a point, Rick. If the ignitor glows, the pressure switch is closed. If the OP was using a meter and reading across the terminals, he's going to see zero voltage, because he's reading across the line.

All the safeties are closed. The gas valve does not seem to be opening.

True but all of the limit switches are between the board and the gas valve so it cant hurt to check them . The second thing to look at before tossing parts at it is the LED code but I would reset all the limits/safeties first and go from there .

Rick

 

[koditten]

Is there a down draft sensor on the flue? I had this happen a while back, my push button switch is located in a very odd place, in the back of the unit. Look around for a little button that has a stem popped out about 3/8 of an inch. push it in and this will close the circuit.

Sometimes when the outside air pressure is low or really windy, the switch can trip.

 

[phbsales]

True but all of the limit switches are between the board and the gas valve so it cant hurt to check them . The second thing to look at before tossing parts at it is the LED code but I would reset all the limits/safeties first and go from there .

Rick

I agree with checking it out before throwing parts at it, Rick.

 

[phbsales]

Is there a down draft sensor on the flue? I had this happen a while back, my push button switch is located in a very odd place, in the back of the unit. Look around for a little button that has a stem popped out about 3/8 of an inch. push it in and this will close the circuit.

Sometimes when the outside air pressure is low or really windy, the switch can trip.

Not on a condensing furnace. There's a flame roll-out switch at the burner compartment that will kill the flame if it is venting improperly.

 

[All Systemz]

Doesn't sound like your checking for 24v properly.
If it get's as far as the ignitor glowing, then you have 24v at ALL limit switches and pressure switch.
Depending on how long the gas line is, maybe it's not purged enough.
Cycle it over and over and I bet it will fire.

 

[trbomax]

I went back thru the startup proceedure again and I found that I neglected to prime the condensate line/trap. So, I filled it and it fired right up. Could the pressure that closes the switch been going out the condensate line ? If so its really sensitive.

My flames look good,soft,semi pointed and all blue.

The only thing now is thhat the temp rise is weak at 18 degrees. This could be because the return air from her shop is being pulled out of my clean room which is not walled in or heated. I would think it should be more like 30 deg but I'm not going to get tooexcited about it untill I can isolate her return.

 

[All Systemz]

I'm guessing this is a new or pretty new furnace if it's 96%.
If so, the trap would not have to be filled for it to fire.
We install these all the time and never fill/prime the traps.

Did you check/adjust the gas pressure at the manifold now that it's firing?
I bet it's low and why your temp rise is low.

 

[brewchief]

I'm guessing this is a new or pretty new furnace if it's 96%.
If so, the trap would not have to be filled for it to fire.
We install these all the time and never fill/prime the traps.

Did you check/adjust the gas pressure at the manifold now that it's firing?
I bet it's low and why your temp rise is low.

I've run into a few that needed the trap primed before they would run, mostly they will start and run for 5-10 min fine then shut off because it's not draining properly.

Furnace was converted to LP correct? Don't skip setting gas pressure, instructions with the LP kit may say to turn in the regulator screw X amount of turns for a starting point, that will get it close enough to light up but that's about it.

 

[trbomax]

Its new, and I dont have any way to check the gas pressure. I was going to get the local furnace guy out here to do it .

 

[theoldwizard1]

Look at your sequence of operation. Combustion blower starts allowing the pressure switch to close, allowing the ignitor to glow. Final steps are gas valve opens and flame is proved.

You either have a bad gas valve, or gas pressure is not set properly.

Your sequence of events is not correct.

Draft blower
Sense draft
Igniter
Sense Igniter
Gas valve open
Sense flame or shut valve

My furnace requires the igniter temperature sensor to be cleaned every year or 2.

 

[jimp]

Where did you purge the gas line?

 

[D.J.]

Could it not have just been air in the lp supply line that is now delivering lp correctly on the initial start up cycles?

 

[trbomax]

no,the valve was not pulling in. I can feel the "click" nowafter i filled the trap it went thru 3 cycles , then lit up . second cycle it puffed a bit so that was the air.

 

[phbsales]

Your sequence of events is not correct.

Draft blower
Sense draft
Igniter
Sense Igniter
Gas valve open
Sense flame or shut valve

My furnace requires the igniter temperature sensor to be cleaned every year or 2.

You realize that the flame rod does not sense heat, right? It detects the micro-amp electric signal created by the flame.

Also, on a Goodman furnace, even if the ignitor is an open circuit electrically, the gas valve will still open until the flame sensor faults. There is no ignitor sensor.

Please do not attempt to discredit me on the open forum. If you have a problem with my methods, feel free to PM me. I'm always willing to learn something.

 

[theoldwizard1]

You realize that the flame rod does not sense heat, right? It detects the micro-amp electric signal created by the flame.

Technically you are probably correct.

The bottom line for me is, if my furnace (Carrier) doesn't start (gas valve does not open), clean the sensor next to the igniter (fine emery cloth). I forgot what the "blinking light" code was.

 

[phbsales]

Technically you are probably correct.

The bottom line for me is, if my furnace (Carrier) doesn't start (gas valve does not open), clean the sensor next to the igniter (fine emery cloth). I forgot what the "blinking light" code was.

It's 34 (flame failure). If it happens 3 times the furnace will lock out on a "14" code and auto reset after 3 hours.

Emery cloth works great, but in a pinch you can use 1000 grit sandpaper or a dollar bill.

 

[theoldwizard1]

It's 34 (flame failure).

So why is it called "flame failure" if the gas valve never even opens ?

Emery cloth works great, but in a pinch you can use 1000 grit sandpaper or a dollar bill.

Same thing the furnace tech told me !

When it happens in the middle of a cold night, I found that cycling the furnace switch will cause the burner to come on immediately. Easier then going into my crawl space and dis-assembling something at 2AM. Of course, I probably have to repeat it at 4AM and 6AM ...

 

[phbsales]

So why is it called "flame failure" if the gas valve never even opens ?

Hell if I know...............LOL

 

[lametec]

Because the flame failed to materialize (or dematerialized after materializing). The control board doesn't know if it's due to a bad valve, no gas or too low pressure. So "flame failure" is a broad description that covers all scenarios.

 

[Hlidskjalf]

Make sure you have the drainage piped in properly. Depending on what side your trap is on you may need to rearrange it. Goodmans are sensitive like that, check your manual.

 

[mrobins297aaa]

make sure you check the gas pressure, some of these new furnaces have a low pressure cutout.