# Tempstar furnace green light flashes 3 times



## zappa (Nov 25, 2011)

> I tried to use a jumper wire on both of the switches but nothing changed.


Is this jumper on the pressure switches? Not much experience with furnaces but I'm pretty sure timing is important with these switches. If the controller sees that the switches are closed when a call for heat comes in, it will fault out.


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## beenthere (Oct 11, 2008)

A cracked heat exchanger can cause the furnace not to fire up, as the pressure switch may not close.


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## supers05 (May 23, 2015)

Some newer furnaces will fault when the pressure switch is jumpered before the call for heat. Older ones didn't care. Make sure your flue vent isn't blocked, or fresh air vent. 

Is it even trying to fire up? Or the spark/hsi not even sparking/glowing? Do the hear the gas valve click? Do you smell gas at the vent outlet? (may be very faint) 

Cheers!


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## mi_fiveo (May 19, 2012)

I do hear a click from the gas valve but nothing happens. Then the light goes from steady to flashing three times. I haven't checked the fresh air pipe yet. I no longer have a jumper wire on the pressure switches. I was just trying to bypass them to see if it would fire up. It didn't change anything.


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## roughneck (Nov 28, 2014)

First, stop jumping everything out. Your meter will tell you all you need to know. 
Verify the heat exchanger is in usable condition before continuing any further.


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## mi_fiveo (May 19, 2012)

Where is the heat exchanger, and how do I verify that it is usable?


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## roughneck (Nov 28, 2014)

The heat exchanger is the part that carry the gasses of combustion from the burners. 
If it's cracked or compromised you'll get CO in the structure, which can very easily kill you


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## mi_fiveo (May 19, 2012)

Any ideas or things to check with the voltmeter?


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## zappa (Nov 25, 2011)

You can check the pressure switch operation. ~zero volts across switch is closed, ~24 volts across switch is open. Same for limit switches in low voltage control.


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## roughneck (Nov 28, 2014)

Thought you were going to check the heat exchanger?


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## mi_fiveo (May 19, 2012)

I don't know what it looks like or what to remove to get to it. 


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## roughneck (Nov 28, 2014)

Well don't ignore it because of that. That's a good way to wind up as the top story on your local news. 
A good combustion analyzer would be able to pick up an issue. You might also feel air blowing back out of the burners with the blower running, or see the flames from the burners be pushed back out of the burner tubes while the burners are firing. 
Unless there's a warranty a bad heat exchanger means the death of the unit. And it cannot run with a bad heat exchanger


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## zappa (Nov 25, 2011)

How far along is your furnace getting to?

1) Exhaust fan on
2) Glow or spark ignition
3) Gas valve open
4) Flame
5) Blower motor starts


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## supers05 (May 23, 2015)

A cracked or plugged heat exchanger often will still make the pressure switch. It'll usually trip the flame sensor or roll outs. A plugged Heat exchanger could trip a double switch, but not every unit has one. (only makes within a specific pressure range. Too high or low and it breaks.) OP, you'll be able to tell, by if it has 2 pressure ratings on the pressure switch. (or 2 switches for a single stage, or 4 switches for a dual stage) 

PS. I use a manometer to test heat exchanges. They are rated for a specific pressure across them, anything higher or lower means a problem. It'll detect problems way before an flue analyzer

Cheers!


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## mi_fiveo (May 19, 2012)

zappa said:


> How far along is your furnace getting to?
> 
> 1) Exhaust fan on
> 2) Glow or spark ignition
> ...



The exhaust fan was running continuous regardless of the thermostat and no heat. I replaced the main board then the exhaust fan stopped running continuously but the blower fan ran steady. I reset the button on the limit switch and now it stopped also. When I turn the stat to heat the exhaust fan does not turn on and nothing else happens.
I hear a click from the gas valve. The green light starts flashing three times. So it doesn't get to any of those stages. 
.










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## mi_fiveo (May 19, 2012)

supers05 said:


> A cracked or plugged heat exchanger often will still make the pressure switch. It'll usually trip the flame sensor or roll outs. A plugged Heat exchanger could trip a double switch, but not every unit has one. (only makes within a specific pressure range. Too high or low and it breaks.) OP, you'll be able to tell, by if it has 2 pressure ratings on the pressure switch. (or 2 switches for a single stage, or 4 switches for a dual stage)
> 
> PS. I use a manometer to test heat exchanges. They are rated for a specific pressure across them, anything higher or lower means a problem. It'll detect problems way before an flue analyzer
> 
> Cheers!



There are two pressure switches that I can see. 



















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## supers05 (May 23, 2015)

Make sure the little on/off button on the gas valve is set to "on". Check that the black tubes on the pressure switch are clear. Check with a meter across the 2 terminals of the low pressure switch. It's pic #1 for me, without anything in front of it. It should read 24ish v across, before it venter motor starts. 0v when it's running. Also check the aux high limit. 

Cheers!


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## yuri (Nov 29, 2008)

The exhaust fan needs to run before the pressure switch closes. It closes to prove it is running. Check for power at the exhaust fan when the thermostat is calling for heat.


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## mi_fiveo (May 19, 2012)

I'll check those things when I get home and post the results. Thanks for the suggestions!


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## mi_fiveo (May 19, 2012)

The gas valve is set to on. The tubes are also clear. I took each one off and blew air through them yesterday. I have not noticed any glow from the viewing window when I call for heat. Does this mean the flame rod isn't trying to ignite the gas? Or does the furnace not get to this point because the exhaust fan and pressure switch won't allow it?


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## mi_fiveo (May 19, 2012)

Hot surface igniter not the flame rod. What I was referring to. Still learning all these terms. 


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## yuri (Nov 29, 2008)

Sequence of op is this:

1) Thermostat tells the circuit board to turn the exhaust fan on which creates a vacuum on the switch and closes it which tells the gas valve it is OK to open plus the igniter gets power. The switch is doing its proper job w/o a vacuum.


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## mi_fiveo (May 19, 2012)

Put the old board back in as a last ditch effort. Fired right up. Limit switch being tripped must have been the problem the whole time. New board I ordered must have been faulty. You would think the dumb hvac guy I had come to my house would think to reset the limit switch. Nope, your furnace is not fixable, you need a new one. Shady people out there. Thanks for the help everyone. 


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## zappa (Nov 25, 2011)

Limit switches don't trip for no reason. Is it a roll out or heat limit? Did he mention anything about a cracked heat exchanger?


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## supers05 (May 23, 2015)

It sounds like a roll out. If that's the case, your heart exchanger is probably bad. It would be a good reason to condemn the furnace. However, there are lots of shady guys out there.... 

Cheers!


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## mi_fiveo (May 19, 2012)

It was a limit switch that was tripped. No idea why. 


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## roughneck (Nov 28, 2014)

Not usual to just have one trip. There's usually a root cause behind a tripped limit and/or rollout. 
As I said before, a cracked heat exchanger presents both a fire hazard and a carbon monixide danger. Be sure you don't have either.


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## beenthere (Oct 11, 2008)

Looks more like a roll out switch then a limit. Which may indicate that you have a heat exchanger problem.


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## supers05 (May 23, 2015)

Most common is as a rollout, though I've seen those types as limits too. Especially on blower housings. OP: post a picture of where it is on your furnace. 

Cheers!


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## mi_fiveo (May 19, 2012)

The switch is mounted on the right side of the silver box with the viewing window. 200 degree switch. If I remove the front cover will I be able to inspect the heat exchanger?


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## yuri (Nov 29, 2008)

Yes. It is very common for them to crack where the flames enter the heat exchanger after the burners on that model. The rest of it would require a highly experienced Pro who knows that furnace and brand if it is cracked lower or has other problems.


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## supers05 (May 23, 2015)

If it's on the side of the box that sticks out a bit there, (burner fresh air cover) it will be a roll out. A limit would be on the panel that the box is attached to. There a slight slight chance that it was a fluke back draft or something like that, but most likely for heat exchanger is defective. If it is, it's time for a new furnace. (unless it's under an extended warranty) 

Cheers!


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## mi_fiveo (May 19, 2012)

Thanks for all the help and suggestions. I'm going to remove that cover and see if I can see anything cracked or obviously wrong. I'll post pics when I get some time to do it. 


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## beenthere (Oct 11, 2008)

You generally can't see the cracks from that area. You often can see the flames blow back when the blower kicks on while the burner is on.


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