Tempstar furnace won't turn on

Johnny_

Circuit board problem. Furnace every few weeks wont turn on, i can get it to turn on by unplugging, plugging back in the main connector plug on the control board. Board is Honeywell ST9162A
When i unplug it, i think i hear a relay click, which tells me a relay is sticking. Worth replacing the relays? I tried replacing the whole board but i used a used board and am still having same problem.
Any help would be great!

Ironman

You're probably experiencing a safety lockout and there's no problem with the board. Interrupting the power resets the board but doesn't correct the cause.

That board is used with the Honeywell SmartValve. Is there an LED flashing a code?

Here's a link to its service instructions:

https://customer.honeywell.com/resources/techlit/TechLitDocuments/69-0000s/69-1237.pdf

JUGHNE

Simple but not obvious; I have had some blower door safety switches have intermittent problems. When/if you have no heat and open that door to inspect, and reclose it you might reseat that switch and also you power down and back up which would reset a lockout condition.

When I get a dead furnace call I go to the T-stat and try the fan switch. If the blower comes on then that confirms several things:
120 VAC to furnace
Blower door switch is OK
24 VAC is OK
The R and G wire at least are intact

Older HW Smart Valves had problems with the main molex connector plug. Yours sounds fairly new being 2 stage.

Abracadabra

I'd be wondering if the used board had the same problem. I'd use a new board.

Johnny_

Im away from home working unfortunately so i cant work on it now. I do remember it had a fault code on the smartvalve. It was 8 beeps i tthink. The fault code said pressure switch stuck.

Ironman

JUGHNE said:

When I get a dead furnace call I go to the T-stat and try the fan switch. If the blower comes on then that confirms several things:
120 VAC to furnace
Blower door switch is OK
24 VAC is OK
The R and G wire at least are intact

That's the same same thing that I've done and taught my mechanics for over thirty years. In a few seconds, you've eliminated several potential causes that would take 30 minutes to check individually.

It also confirms:
1. The blower runs
2. The fan relay or board is calling for the blower to run.

It works for diagnosing A/C, too.

Ironman

Johnny_ said:

Im away from home working unfortunately so i cant work on it now. I do remember it had a fault code on the smartvalve. It was 8 beeps i tthink. The fault code said pressure switch stuck.

Then chances are you have a blocked flue inlet or outlet or the condensate drain is plugged if it's a 90+ furnace.

Johnny_

From what I remember the main blower would run fine. Its the fresh air or exhaust blower that doesn't turn on until you reset it. The first blower in the sequence that is supposed to turn on.

Thanks!

DZoro

what is the model number of the furnace ?

Johnny_

I'll have to check a few things and get back on Tuesday when im back

Johnny_

Also im sure the flue inlet and outlet are not plugged and i will check condensation line.
I found a picture i took with model number.
T9mpv075f12b1

JUGHNE

Of course the T-stat test only works if you have a heat/cool system which is about 98% of what I see here.

Another item is the doorbell. When wiring a house I usually install the DB transformer on the service switch box for the furnace, connected to the line side of the switch. If the door bell is not working it is possible the CB is off or tripped.

That location also groups most of the low voltage cables in one place and you know the transformer won't get buried above the basement ceiling.

DZoro

You have a internal condensate trap system. Clean and check all the drain tubes to the center trap. Sounds like pressure switch is sticking, furnace is 11 years old, may want to get new pressure switches if venting and drains are all clear of condensate, and there is no blockage of any type. Venting should be sloped to the furnace and both pipes should have clean and clear passages. 1/4" tubes to the switches should not have any condensate in them at any time.

Johnny_

Thanks, i 'll do that.
One more thing i forgot to mention. The board wi llonly succes sfully reset if i pull the cconnector with the power on. I wont work with the ccircuitbreaker off. I wonder why flipping the breaker alone doesnt reset it successfull.

Tim McElwain

Does the unit operate on just low fire? That system will start on high fire then drop to low fire if no hi fire call. There are two pressure switches one for low fire one for high fire. The eight flash usually indicate the hi fire pressure switch is closed when it should be open. Some of these furnaces had problems with the draft inducer not getting up to full speed on high fire. You need to check the pressure differential across the pressure switches the low switch is .58" W.C. and the high switch 1.38" W.C.

What others said about condensate line and secondary heat exchanger need to be looked at.

wogpa67

Was that a current pic of the data plate?

Johnny_

Current picture of data plate yes.

wogpa67

I'd get service done on that then. All the mouse hair bird feathers and stink bugs in that pic! I've filled 5 gallon shop vacs with stink bugs. And you have more going on with your furnace.

wogpa67

Oh and sparky most likely didn't mark the breakers correctly.

Johnny_

Dennis said:

You have a internal condensate trap system. Clean and check all the drain tubes to the center trap. Sounds like pressure switch is sticking, furnace is 11 years old, may want to get new pressure switches if venting and drains are all clear of condensate, and there is no blockage of any type. Venting should be sloped to the furnace and both pipes should have clean and clear passages. 1/4" tubes to the switches should not have any condensate in them at any time.

I cleaned out the condensate trap. Will see if it happens again. Tough part is it only stops working once every few weeks.
I am correct to say pressure switches should be not the problem since it's the first fan that won't turn on (the venting fan I believe it's called).
I checked the 1/4" tubes and they do not have condensate in them.

Johnny_

Tim McElwain said:

Does the unit operate on just low fire? That system will start on high fire then drop to low fire if no hi fire call. There are two pressure switches one for low fire one for high fire. The eight flash usually indicate the hi fire pressure switch is closed when it should be open. Some of these furnaces had problems with the draft inducer not getting up to full speed on high fire. You need to check the pressure differential across the pressure switches the low switch is .58" W.C. and the high switch 1.38" W.C.

What others said about condensate line and secondary heat exchanger need to be looked at.

When the furnace does not work, the draft inducer fan does not turn on at all, once molex connector is reset, the whole thing works.

DZoro

Johnny,
When the furnace does not work, the draft inducer fan does not turn on at all, once molex connector is reset, the whole thing works.

What is the code/gas valve doing at that time?

Tim McElwain

The power for the draft inducer goes from the board to the gas valve and then from the gas valve back to the board on inducer in - then out to the inducer on low and high. Simply trace the 120 volts from one to the other to the other. On the gas valve there is an internal switch that can be faulty between C3 Pin 1 and C3 pin 2. That is what powers the draft inducer circuit by sending 120 volts to inducer in terminal on the board the board then sends 120 volts out on inducer low and inducer high.

Johnny_

Dennis, that is correct. The smart valve has a 8 beep code at the time. Which is pressure switch stuck code.
I don't think it is the switch though because the switch is testing the fan flow, which is not even on. Correct?

Johnny_

Thanks Tim, I will have to wait until it quits working again to check out the voltage.

DZoro

What I was asking is when you found the furnace not working did you always see a light at the valve? Fire in chamber?

The board does send power to the valve via the molex connector. Loose or poor connection there would cause no light/power at the valve.
Still looking at the pressure switch. That furnace has 2 switches the top switch is the high fire switch. You can actually disconnect it and the furnace will work but only in low fire. Which is probably if size correctly 90% of the time. With that being said, your problem will only arise when you need second stage. It will flash 8 and still run in low fire as long as the bottom pressure switch is ok. The furnace probably wont maintain your house at your setpoint temp tho.
Are you on LP gas? If so there is another pressure switch involved also. That one should be wired to the bottom switch if installed correctly.
Are you able to ohm out the switches? That is really what should be done first. Do this during all stages of operation, low, high, and off

Johnny_

When the furnace does not work, from the first time it happened, the valve blinks with the 8 code. During that time, there is no fire in chamber and no inducer motor running. There is a call for heat from the T-stat.
I just ran the furnace and timed:
everything was normal up until 12 minute mark, something turned up higher (not the main blower fan, was either the gas or the inducer) however after one minute of that, the flame shut off completely, the blower stayed on low and then it begun a normal low cycle again.
This is different from the times it does not work however. When it does not work there is no flame at all and no inducer at all until molex is reset.

Johnny_

Natural gas

Johnny_

In middle of cycle, 12 minute mark, I am getting a 4 beep code.
Which is:
Main Limit or Roll Out Switch is open.
Combustion blower is energized, Circulating blower is energized
heat speed.
Says to check/repair:
Main limit switch.
Manual reset burner rollout switch.
Limit and rollout switch wiring is in good condition and securely
connected.

Can anyone explain how to do those checks/repair?

Thanks alot.

Johnny_

Or would it be tripping the switch because main blower is not going to high?

DZoro

Sounds like you may have a single stage stat? Is there a wire connected to W2 at the furnace. 12 minute mark usually is a internal timer that if furnace doesn't satisfy at low fire for a set period of time it will automatically go to high fire.
Need to check high fire press switch!
Now you just brought on other issues that may or maynot be related.
The pressure switch should be checked like Tim said!
Filter system checked
Secondary checked, pull blower and clean secondary
Return and supply duct/registers checked, all clear and open.
Combustion checked
Rollout, main limit trips are serious and should be checked by a professional.
There seems to be more going on here than appears from this angle.

Johnny_

Yes it is single stage t-stat.
Fixed the problem of rollout, was a combination of dip switches set low and filter. Am also going to clean the blower also.

icesailor

Abracadabra said:

I'd be wondering if the used board had the same problem. I'd use a new board.

Used control boards are sort of like used condoms. Why take a chance? Because they are cheap?

If you needed a knee or hip replacement, would you spend less for a used cadaver replacement part? Knowingly?

Don_197

the Smart Valves had a known issue.....bit me more than once......no heat call.....walk up to furnace, inducer not running, pressure switch fault. Unplug Molex from gas valve and plug back in.....furnace fires and runs full cycle.....stick around......fires up again runs full cycle......stick around......furnace runs full cycle again. Charge customer minimum service charge as connector was just loose. Two days later.....call back......exact same issue. after this happened to me 3 times I started changing the smart valve out.......no callbacks.

Johnny_

thanks, any idea what a smart valve would cost?

Don_197

Expect to pay $200-300 for the part.......not a DIY project.........have a professional install it......it may save your life.

Tim McElwain

I would suggest before you purchase anything have a professional come and diagnose the problem.