Gas and Oil Home Heating Furnaces - Trane XV80 - No Heat

Well its cold finally here in Texas and tonight the heater on the old XV80 stopped working.

The heat blower runs, the igniter glows, the safeties (5) are all good but the gas valve does not open. The unit shuts down after a few seconds then tries again, then after the third try the fan blower starts and runs with no heat. The coil on the gas valve will pull in if you jump it out. So what is keeping the control board from operating the gas valve?

I bought the house with the unit so I have no documentation except the wiring diagram on the panel that all checks out. There is a red flashing light on the board. I would prefer to see green but I have no indication that red is bad.

The user manual you can find on-line is worthless to troubleshoot with... it has you check the heater condensate drain for a plug... and I read it twice to be sure that is what is said. Well I have no heater condensate drain... nor does the unit look to be set up for one... nor do I believe that is valid troubleshooting step for heat. The next step is to call a service technician.

so I found this site.... I hope to return the favor soon.

Any suggestions.

I bought the house with the unit so I have no documentation except the wiring diagram on the panel that all checks out. There is a red flashing light on the board. I would prefer to see green but I have no indication that red is bad..

How many time is the light flashing before it pause and flash again?

The red light on the board flashes constantly with no pause.

Is the igniter element somehow in the board circuity that controls the gas valve. There are two wires to the igniter element, it glows when powered but I can't tell if its at the correct temperature to fire off the gas. That is the only thing that I cannot meter or test if its working properly. Does the control board measure resistance across the element or something. That element looks a lot cheaper than a new board but I don't want to go replacing components hoping for the right guess.

The red light on the board flashes constantly with no pause.

What is the green LED doing?

With the red LED flashing it's giving an error code, and the info is on back of the blower door with the fault code.

Does the control board measure resistance across the element or something..

Kinda both temp and resistance.

Take your meter, and ohm it out. At room temp, it should read between 40 and 150 Ohm. If you are reading over 100, usely it's time for it to be replaced.

on power up the red light flashes constantly slow - normal
On call for heat the red light flashes fast - normal

after three tries turing on the heat blower and igniter element, the unit blower starts, a green light comes on and the red light flashes twice. The error code is external lockout re-tries exceeded.

the control board seems to be doing its thing...

bad gas valve relay on the control board maybe?

What Ohm reading are you getting on the ignitor?

Were you getting voltage at the gas valve?

You said all safety switch was Ok, (Did you do voltage reading on them or ohm it?)

well at temperature is 54F in the house right now... it measures 16.9 ohms.

safeties were checked with voltage on each leg to ground and conductivity across them.

no voltage at the gas valve. But i jumped 24vac at the circuit board connector to the low stage heat and the coil on the valve pulled in.

Safety wiring leaves the board connector then comes back to the board connector. When the heat blower is running the wire leaving and entering the control board is good.

But i jumped 24vac at the circuit board connector to the low stage heat and the coil on the valve pulled in.

What did/how you jumped?

The inducer fan did not run, and no ignitor?

What is the full model # of this furnace and age?

Are you sure you got 16.9? That is the lowest I have ever seen. Sure you are not at a X10 reading on your meter, and you are really at 169 ohms?

If you are using an analog meter, did you 'zero' it out first before ohms testing? Although, if you really read 16.9, and not estimating the decimal, you must be on a digital one.

Thanks for helping...

I used a jumper from 24vac power to the low stage coil by sliping a wire in the back of the connector on the control board to make the circuit that goes to the valve. The common on the gas valve coil comes back to common on the control board and low comes directly back to the control board as well. Jumping is not exactly by the book, but I am comfortable working on equipment like this... just not that familiar with residential and don't have any technical info on the Trane equipment. I did not hold in the gas valve to verify gas, i just bumped it. That showed me the coil on the valve works. The controller does not send voltage out on this wire when it should. This jump works W/O inducer fan because it bypasses the safeties. Safeties wire come out of the contrller and gos back to the controller.


Model - TUD100R9V5J1

Serial - Z182J232G

Age ?

Rap on the gas valve with the plastic butt end of screw driver repeatedly, when it clicks to try to go. I have gotten 2! furnaces going for the first time this year with that problem. And now they continue to work just fine.

If you are on natural gas and truly no gas comes out, then the 1/4 or 1/2 foot dial on gas meter outside will not move, confirming no gas rather, than lack of ignition.

well it never really clicks to try to go on its own. but I did rap on it a few times already. Gas is on and working. Control board is not sending a signal to open the gas valve when it is supposed to.

For the igniter ohms, I went and got a new ignither and it ohmed at 14.3. I have a digital fluke that auto ranges... not sure of the range now but both old and new ohm nearly the same... and worse i get the same result when the new is in the unit... so it is not the igniter.

On these units that work, does the control board send a signal to open the gas valve at the same time the igniter is lit or sometime after.

If it is sometime after the igniter is lit, what would cause the controller to not signal the gas valve if all the safties are good?

On these units that work, does the control board send a signal to open the gas valve at the same time the igniter is lit or sometime after.

If it is sometime after the igniter is lit, what would cause the controller to not signal the gas valve if all the safties are good?

It signals the gas valve to open quite a number of seconds after the ignitor first clicks on to glow. It allows time for the glow to come up to full brightness//heat, and then the gas valve comes on. I think about 30 seconds from when the ignitor first clicks on. That should give you some idea.

Are you not getting the gas valve signal? I thought you were? Otherwise I have to reread posts.

When the controller should give a gas valve signal... it does not. All safeties are good. The unit tries 3 times and starts the induction fan and lights the igniter each time then fails on a failed to start time out. The unit needs to be re-set via power to try again. If at the time the gas valve is suppose to get a signal from the controller, I jump it out by putting 24vac on the gas valve wire leaving the controller, the unit fires up and provides heat as if normal... but the next failure code after the flame lights is flame detected when there should not be flame.

If it was a gas relay on the board that was bad, then it should not be giving a flame error. So the controller seems to be keeping the gas valve off for a reason.

I need a flow chart of how the controller works. I am not convinced its a bad controller....

Any ideas would help.

I believeyour ignitor is bad even though it is glowing. If the circuit impedence is not within specified range the controller will not let the gas open. I ran into this on an oven. I'm not 100% sure it applies to your furnace but based on my experience Thats my two cents.

I replaced the igniter today with the factory Trane replacement part and it does the same thing.

I have a 3 flash Diagnostic Code that says Pressure switch Error ....what do i do ?

I have a 3 flash Diagnostic Code that says Pressure switch Error ....what do i do ?

YOu got the XV80 as well?

Make sure the exhaust pipe is not blocked.

Undo the hose from the pressure switch, and blow into it.

Hi -
I've ran in to the exact same problem with XV-80 unit at my home.
I am curious to know what did you end up doing for solving the problem.
Thanks

Hello Snoop--

My suggestion is to start a new thread and describe in detail what problem you are seeing and what the furnace is doing.

There are lots of possible defects with a furnace, and guessing that you have the same problem is not likely to be the case.