Furnace seems stuck in lockout mode after power outage

Alix · January 20

Hello,

I have a Trane XV90 forced air furnace that seems to be stuck in lockout mode. I'm seeing the error code "two green flashes and then two red flashes," which I think means "open high limit switch." The furnace was working properly until a tree knocked down our overhead electrical service during an ice storm and we lost power. Power is now restored, but now we need to get the heat going. The furnace goes through the motions of starting up but seems to cut out after the warm glow appears in the upper sight glass. (It does not have a pilot light.) It repeats this a few times and then seems to give up. The fan then kicks on and it blows the cold air through the ducts.

I don't see a reset button. I tried resetting it by turning the power off for a minute or two and then turning it back on, but get the same result. Also, the natural gas shutoff valve doesn't have a lever so I'm not a 100% certain it is in the optimal position. I'm including photos below. Does the control board look okay? Is there anything else I can try?

Jamie Hall · January 20

The high limit switch may be a manual reset switch -- or worse, a one shot. Have you located it and checked to see?

Otherwise if there was a voltage surge when the tree interfered, you may have a fried control board.

Big Ed_4 · January 20

The first check for a tech is to see if you have fuel ...

Cooper1957 · January 20

If the furnace was working prior to the power outage you can probably rule out the gas shut off valve. What you do need however is a multi meter to check the other components. One possible problem is the hot surface ignitor is not producing the required " heat" for ignition. Without a multi meter we are just guessing.

Alix · January 20

Jamie Hall said:
The high limit switch may be a manual reset switch -- or worse, a one shot. Have you located it and checked to see?

Otherwise if there was a voltage surge when the tree interfered, you may have a fried control board.

I have not been able to locate the high limit switch. I was hoping to find it so I could try a manual reset if there was one.

Alix · January 20

Cooper1957 said:
If the furnace was working prior to the power outage you can probably rule out the gas shut off valve. What you do need however is a multi meter to check the other components. One possible problem is the hot surface ignitor is not producing the required " heat" for ignition. Without a multi meter we are just guessing.

Initially I thought I smelled gas so I turned the gas shut off valve. I'm not 100% sure I put it back in the correct position. I will try to get my hands on a multi meter.

Mark Eatherton · January 21

If your furnace was firing at the time of the power loss, the heat exchanger had a lot of heat in it, and when it rises up, it causes the manual reset high limit switch to open. I believe if you look between the two bright yellow wires in the picture, you will find a small reset button. Push that and it should refire. Your gas valve shown is open, The two dots on opposing corners of the gas cock show the position of the close off. Parallel to the pipe is open, right angle to pipe is closed.If the high limit is fried, you can bypass it temporarily until you get a new one, but do not leave it bypassed under penalty of death and or fire.

Alix · January 21

Mark Eatherton said:
If your furnace was firing at the time of the power loss, the heat exchanger had a lot of heat in it, and when it rises up, it causes the manual reset high limit switch to open. I believe if you look between the two bright yellow wires in the picture, you will find a small reset button. Push that and it should refire. Your gas valve shown is open, The two dots on opposing corners of the gas cock show the position of the close off. Parallel to the pipe is open, right angle to pipe is closed.If the high limit is fried, you can bypass it temporarily until you get a new one, but do not leave it bypassed under penalty of death and or fire.

Thank you very much! You are right, if you follow the two yellow wires, it leads to a small red reset button. I pressed on it, and it didn't feel like it moved at all, and the furnace didn't refire. It makes me think that it had not actually tripped. I guess this switch is called the "flame roll out switch." Is it possible that the "high limit switch" is the one behind the flame rollout switch in the photo below:

mattmia2 · January 21

I'm not sure you're reading the flashes right. Might want to read the manual. Maybe it is only the 2 red flashes and failure to prove flame which sounds more like what's happening.

109A_5 · January 21

Hello @Alix,
As @Big Ed_4 said, are you sure you have gas ? Seems like fuel is missing.

EBEBRATT-Ed · January 21

Yes the high limit is the one attached to the furnace with the two screws. Not the one with the reset button. Try jumping the two yellow wires on the HL.

As Mark said this is fir troubleshooting only you can warm up the house if it works but DO NOT LEAVE IT JUMPED>

Can you post a picture of the wiring diagram?

Alix · January 21

mattmia2 said:
I'm not sure you're reading the flashes right. Might want to read the manual. Maybe it is only the 2 red flashes and failure to prove flame which sounds more like what's happening.

That could be the case. Here is what the installer's guide says:

Alix · January 21

109A_5 said:
Hello @Alix,
As @Big Ed_4 said, are you sure you have gas ? Seems like fuel is missing.

Gas is flowing to our hot water heater and the burners on our cooktop. I can't say for sure whether it is flowing properly to the furnace, although I was told the furnace's gas shutoff valve is in the correct position for gas to flow.

Alix · January 21

EBEBRATT-Ed said:
Yes the high limit is the one attached to the furnace with the two screws. Not the one with the reset button. Try jumping the two yellow wires on the HL.

As Mark said this is fir troubleshooting only you can warm up the house if it works but DO NOT LEAVE IT JUMPED>

Can you post a picture of the wiring diagram?

Thank you very much -- I'd like to try your suggestion. Could you clarify what you mean by "jumping" the two yellow wires?

The wiring diagram on the panel is in rough shape. I'm including that below along with the ones in the installer's guide. I looked online for wiring diagrams for our model, TUY100R9V4W1 (aka UY100R9V4W1),
and haven't found anything yet...

mattmia2 · January 21

I wonder if the control board has been replaced and the label and manual dont apply to that board.

Alix · January 21

mattmia2 said:
I wonder if the control board has been replaced and the label and manual dont apply to that board.

Thank you, yes, that could very well be the case. I think the previous owners did a lot of work on the furnace. I will look through the records.

Alix · January 21

Alix said:

mattmia2 said:
I'm not sure you're reading the flashes right. Might want to read the manual. Maybe it is only the 2 red flashes and failure to prove flame which sounds more like what's happening.
To be more precise, the flashes are actually as follows:

Green
Green
Red
Red & Green simultaneously

So, a total of 4 flashes, unless the flash of red & green simultaneously counts as more than one.

109A_5 · January 21

Hello @Alix,
Do you hear the gas valve click assuming the control board tries to open it ?

With a multi-meter you could tell if the control board is even getting to that point 24 VAC across the gas valve's terminals and you can also test the continuity of the other limits and sensors.

109A_5 · January 21

Hello @Alix,
BTW, none of the documentation I've seen so far mentions a Bi-Color LED. So I'm thinking the Green is possibly acknowledging the call for heat and the Red is the Error Code.

Alix · January 21

109A_5 said:
Hello @Alix,
Do you hear the gas valve click assuming the control board tries to open it ?

With a multi-meter you could tell if the control board is even getting to that point 24 VAC across the gas valve's terminals and you can also test the continuity of the other limits and sensors.

I definitely hear a clicking sound where the gas valve is located, and around that time I can smell a faint whiff of gas. I'm planning to head out soon to pick up a multi-meter.

Alix · January 22

Hello @EBEBRATT-Ed, I used a makeshift jumper wire on the high limit yellow wires as shown in the image below, and then powered on the furnace. It continued doing the same thing it has been doing (it goes through the motions of starting up but cut outs after the warm glow appears in the upper sight glass). Also, I did pick up a multi-meter. I guess that's the next thing to try? Or should I try cleaning the flame sensor first?

mattmia2 · January 22

There is no flame to sense, it isn't getting that far

109A_5 · January 22

Hello @Alix,
Measure one at a time during an attempt to start the furnace, while the hot surface igniter is glowing measure MV COM to MVH then MV COM to MVL to see if any power from the control board is attempting to open the gas valve. I'm not sure if it starts off in Low or High fire.

Mark Eatherton · January 22

Is the blower door closed? I think there'a safety switch there too...

mattmia2 · January 22

Was this furnace made after emerson bought white rodgers? If not that board is a replacement and you need to find the instructions for it.

Alix · January 22

mattmia2 said:
Was this furnace made after emerson bought white rodgers? If not that board is a replacement and you need to find the instructions for it.

The furnace was installed in 2003. Google says Emerson acquired White Rodgers in 1961, but it seems they may not have "merged" until 2015 during a strategic reorganization.

Alix · January 22

Mark Eatherton said:
Is the blower door closed? I think there'a safety switch there too...

Yes, I've had the blower door closed. Is the safety switch in there something to measure, or might it have a reset button that could be a quick fix?

mattmia2 · January 22

I think you're going after the wrong code, i think you are failing to prove flame or draft.

HomerJSmith · January 22

The furnace was working properly until a tree knocked down our overhead electrical service during an ice storm and we lost power.

I always ask when a incident like this happen, is any thing else in the house acting strangely, burned out light bulbs or something else not functioning properly?

If the neutral wire is disconnected first in the mishap and the phase wires remain connected, you will have 220V going thru everything connected and operating that would normally operate on 110V. It's called a dropped neutral, in which case the board is fried.
As further note, I think that the gas union should be outside of the cabinet, not inside.

MaxMercy · January 22

HomerJSmith said:
I always ask when a incident like this happen, is any thing else in the house acting strangely, burned out light bulbs or something else not functioning properly?

The other thing I think of is whether someone ran a portable generator to power the house.

Alix · January 22

HomerJSmith said:
The furnace was working properly until a tree knocked down our overhead electrical service during an ice storm and we lost power.
I always ask when a incident like this happen, is any thing else in the house acting strangely, burned out light bulbs or something else not functioning properly?

If the neutral wire is disconnected first in the mishap and the phase wires remain connected, you will have 220V going thru everything connected and operating that would normally operate on 110V. It's called a dropped neutral, in which case the board is fried.
As further note, I think that the gas union should be outside of the cabinet, not inside.

All the other electrical items in the house are functioning normally after the power was restored.

Alix · January 22

MaxMercy said:

HomerJSmith said:
I always ask when a incident like this happen, is any thing else in the house acting strangely, burned out light bulbs or something else not functioning properly?

The other thing I think of is whether someone ran a portable generator to power the house.

I did not run a portable generator to power the house after this incident. However, the house does have a generator hookup available, and that may have been used years ago.

mattmia2 · January 22

I think these are your instructions:
https://www.copeland.com/documents/50v54-820-instructions-en-5124596.pdf

Alix · January 22

Thank you very much everyone for your help! I'm learning a lot as always. The furnace repair person was just here. He said the control board was NOT sending power to the gas valve in HIGH flame/heat (the high heat relay is not working). And he said the furnace had been jumpered to run at HIGH flame/heat at all times. He said the control board DOES send power to the gas valve in LOW flame/heat, so he was able to get the furnace to produce heat, but just in low flame/heat.

He said the power outage could have damaged the control board, and that it would need to be replaced to be able to restore the high heat. Unfortunately, the control board for this unit is apparently only sold as part of a kit with a few other high priced items, and so the kit would cost about one quarter to a third of the cost of a new furnace. He said we might be able to get by with low flame/heat for a while. I wonder if there might be a way to purchase a control board without the kit?

mattmia2 · January 22

it looks like it comes with an ignitor but i doubt that is the expensive part:
https://www.supplyhouse.com/White-Rodgers-50V54-820-Trane-Replacement-Two-Stage-Furnace-Control-Kit-for-80V-120V-Hot-Surface-Ignition-Variable-Speed-Blower-Motors

Unless they did a much better job on sizing than most installers do, it probably exceeds your heat loss on low fire.

mattmia2 · January 22

Oh, you might want to trace the wire back from the high terminal of the gas valve to the control board to see if it got spliced in the board transplant and maybe is disconnected somewhere. Look at the connector to make sure the terminal isn't loose in the housing too.

Alix · January 23

mattmia2 said:
it looks like it comes with an ignitor but i doubt that is the expensive part:
https://www.supplyhouse.com/White-Rodgers-50V54-820-Trane-Replacement-Two-Stage-Furnace-Control-Kit-for-80V-120V-Hot-Surface-Ignition-Variable-Speed-Blower-Motors

Unless they did a much better job on sizing than most installers do, it probably exceeds your heat loss on low fire.

You are all awesome, thanks! Now that I have heat I'm planning to return to the furnace project tomorrow, and I'm sure I'l have lots of follow up questions

Alix · January 23

mattmia2 said:
Oh, you might want to trace the wire back from the high terminal of the gas valve to the control board to see if it got spliced in the board transplant and maybe is disconnected somewhere. Look at the connector to make sure the terminal isn't loose in the housing too.

Thank you very much for this suggestion! I look forward to trying this hopefully tomorrow after I get caught up on work!

Alix · January 24

mattmia2 said:
it looks like it comes with an ignitor but i doubt that is the expensive part:
https://www.supplyhouse.com/White-Rodgers-50V54-820-Trane-Replacement-Two-Stage-Furnace-Control-Kit-for-80V-120V-Hot-Surface-Ignition-Variable-Speed-Blower-Motors

Unless they did a much better job on sizing than most installers do, it probably exceeds your heat loss on low fire.

SupplyHouse said that item is discontinued, and that I would need to replace the board and inducer: https://www.supplyhouse.com/Trane-KIT16582-Draft-Inducer-Kit

109A_5 · January 24

Hello @Alix,
If you Google 50V54-820 there appears to be other sources that have the board in stock at various prices.

Furnace seems stuck in lockout mode after power outage

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