Direct vent wall furnace not heating up


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Old 10-18-07, 10:24 AM
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Direct vent wall furnace not heating up

Hello all,

Looks like the attached image. Tried to turn on the heater in anticipation of the coming winter, but it won't heat up. The pilot is lit and stays lit, but when I slide the thermostat temperature setting up, it doesn't turn on.

I've replaced the thermostat with a new one and still the same result. Only two wires go into the thermostat. I've inspected the 3 wires going into the furnace and they appear to be fairly secure.

I've read posts about replacing the thermocouple, but not sure if I'm looking in the right direction. Also not sure if its safe to disconnect the wires going in to the furnace and reattach. Are these low/milli volt, or 110V?

Any suggestions? Thanks!
 
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Old 10-18-07, 11:46 AM
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Originally Posted by DoAsFan View Post
Hello all,

Looks like the attached image. Tried to turn on the heater in anticipation of the coming winter, but it won't heat up. The pilot is lit and stays lit, but when I slide the thermostat temperature setting up, it doesn't turn on.

I've replaced the thermostat with a new one and still the same result. Only two wires go into the thermostat. I've inspected the 3 wires going into the furnace and they appear to be fairly secure.

I've read posts about replacing the thermocouple, but not sure if I'm looking in the right direction. Also not sure if its safe to disconnect the wires going in to the furnace and reattach. Are these low/milli volt, or 110V?

Any suggestions? Thanks!
You'll need to see if there is a power supply to the furnace to find out if it's 110v or millivoltage. Does it have a circulating fan? If yes, then it's 110v. If it's a millivoltage system, you might not be aware that it takes a special thermostat designed for millivoltage systems. So, you can't install any old thermostat. The thermostat you removed- was it the original? If the pilot is staying lit, then the thermocoupe is okay. Are you sure you have the valve knob turned on properly? Try taking the wires that go to the thermostat and jumper them at the furnace and see what happens.
 
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Old 10-19-07, 09:55 AM
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Thanks for the reply. Even when I touch the two wires in the thermostat together, the heater doesn't heat up (gas doesn't turn on).

Is the thermocouple a possible issue if the pilot is lit and stays lit? Everything I'm reading is telling me that the thermocouple is a safety to shutoff gas if the pilot isn't lit. If the pilot is still going, that leads me to be believe that the thermocouple is working and it detects a flame, so gas is flowing.

Could cleaning the thermocouple help?

Thanks!
 
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Old 10-19-07, 02:04 PM
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Originally Posted by DoAsFan View Post
Thanks for the reply. Even when I touch the two wires in the thermostat together, the heater doesn't heat up (gas doesn't turn on).

Is the thermocouple a possible issue if the pilot is lit and stays lit? Everything I'm reading is telling me that the thermocouple is a safety to shutoff gas if the pilot isn't lit. If the pilot is still going, that leads me to be believe that the thermocouple is working and it detects a flame, so gas is flowing.

Could cleaning the thermocouple help?

Thanks!

You're correct. The thermocouple's job is to prove that a pilot flame is available to light the main burners when gas flows to them. So if you have a steadily burning pilot, the thermocouple is ok. Have you been able to determine whether or not you have a milivolt system or a 110v system? Did you try jumpering the thermostat wires at the furnace? Jumpering at the the thermostat doesn't eliminate the wiring between the stat and the furnace as the culprit. Can you find a model or part # on the gas valve?
 
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Old 10-19-07, 02:35 PM
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Not at location to confirm brand/model, but will take not and try to look that up also. I haven't tried jumpering at the furnace.... I see three screws/wires, two which look like the thermocouple connections, with an extra wire coming out of it... not sure where it runs to... assuming it goes to the thermostat along with the third connection.

My only concern with jumpering at the furnace is the fear of 110V, but I suppose I'll have to dig up my multimeter and see.
 
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Old 10-19-07, 07:31 PM
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Hopefully this is not the problem, I have found numerous direct vent wall furnaces with plugged burner orifices due to spider nests
 
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Old 10-20-07, 10:47 AM
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Originally Posted by DoAsFan View Post
Not at location to confirm brand/model, but will take not and try to look that up also. I haven't tried jumpering at the furnace.... I see three screws/wires, two which look like the thermocouple connections, with an extra wire coming out of it... not sure where it runs to... assuming it goes to the thermostat along with the third connection.

My only concern with jumpering at the furnace is the fear of 110V, but I suppose I'll have to dig up my multimeter and see.

You need to clatrfy the voltage issue before you can move on. How many wires are there at the themostat? A wired thermocouple sounds like it'a millivolt gas valve.
 
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Old 10-23-07, 08:42 AM
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Make/Model and Millivolt CONFIRMED!

Its a "Perfection Schwank," model appears to be PDW850-SEM-1.

There is a label on it that says "Millivolt Only." The $10thermostat I picked up at Orchard Supply Hardware says it works for millivolt heat-only systems.

I vacuumed throughly, removed the thermocouple, cleaned it off a little, and reinserted. Lit the pilot per instructions with no trouble. It still stays lit, but no heat!

I guess the next step is replacing the thermocouple, since I've been hearing/reading different reports on how that might affect gas flow. If that doesn't work, then the gas valve, but that might be a little more advanced than I'm ready for.

Haven't been able to locate a manual via Google yet. Did Perfection get absorbed into Schwank Group?
 
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Old 10-23-07, 09:37 AM
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Perfection Schwank now defunct

Schwank Group 1-877-446-3727 pointed me over to Kent H. over at Texas Infrared 1-281-445-1700, which bought up all the surplus parts when the plant closed down six years ago.

Kent was very helpful and suggested that with my symptoms, I either had a bad pilot generator (which I now understand is a thermocouple) or a bad millivolt gas valve.

To test this I've been instructed to try and determine the voltage across the thermocouple. He said that the pilot generator needs to be able to generate 250-300mV to get the gas valve to open. If I'm under 250, then I'll need a new pilot generator (~$30) and if I'm in or over that range, I'll likely need a new millivolt gas valve (~$100+).

Any further suggestions before I go blow myself up?
 
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Old 10-23-07, 01:39 PM
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Originally Posted by DoAsFan View Post
Schwank Group 1-877-446-3727 pointed me over to Kent H. over at Texas Infrared 1-281-445-1700, which bought up all the surplus parts when the plant closed down six years ago.

Kent was very helpful and suggested that with my symptoms, I either had a bad pilot generator (which I now understand is a thermocouple) or a bad millivolt gas valve.

To test this I've been instructed to try and determine the voltage across the thermocouple. He said that the pilot generator needs to be able to generate 250-300mV to get the gas valve to open. If I'm under 250, then I'll need a new pilot generator (~$30) and if I'm in or over that range, I'll likely need a new millivolt gas valve (~$100+).

Any further suggestions before I go blow myself up?
I know better and I used the wrong word, sorry. A t-couple is a 30mv device, what you have is indeed a pilot generator. I believe your pilot generator is ok, otherwise it would not hold in the safety coil that's inside the gas valve. IOW- the pilot burner would not stay lit. However, measuring the mv it's producing is the correct check to do. The reason I keep urigng you to jump out the thermostat circuit at the furnace is to eliminate that from the equation. You don't want to drop $100 for a gas valve only to find out the problem is in the wiring and/or device that is remote from the furnace. After verifying the pilot generator mv, the next step is to eliminate the t-stat and wiring and see if the gas valve works. If you jump out at the furnace AND you measure the correct millivoltage at the gas valve terminals AND the gas valve won't open, then it's a safe bet to condem the valve. Let us know what you find. Thanks.
 
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Old 10-23-07, 01:58 PM
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I think I read it all here. Id say you do want to make sure you buy the right Pilot generator here they come in 250 mV and also in 750mV. So make sure what one you need here.

bad pilot generator (which I now understand is a thermocouple)
The generator is not a thermocouple. They are not the same.
 
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Old 10-23-07, 02:14 PM
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Pics linked

Temporary link to pictures of my pilot generator and the wiring assembly.

I see three connections, two on the left to the pilot generator, two on the right look like they go into the ground and might be running to the thermostat on the wall.

Any clues? I don't know which ones I'd want to short to eliminate the possibility its the wiring/thermostat.


 
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Old 10-23-07, 02:33 PM
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Originally Posted by DoAsFan View Post
Temporary link to pictures of my pilot generator and the wiring assembly.

I see three connections, two on the left to the pilot generator, two on the right look like they go into the ground and might be running to the thermostat on the wall.

Any clues? I don't know which ones I'd want to short to eliminate the possibility its the wiring/thermostat.


You wouldn't want to short across the PG wires. It looks like the 2 wires with the tag are the PG wires? The 2 solid ones are the ones that go into the ground? Compare what they look like at each end. It's the 2 t-stat wires that you want to bypass. By the way, since milivoltage is so small, [750mv = 3/4 of one volt] you might try cleaning the solid wires at valve first. You'd be amazed at how much trouble a little corrsion can cause.
 
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Old 10-26-07, 06:48 AM
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Problem resolved!

Thanks all for all your suggestions.

Turns out it was a loose connection between the apparatus and the gas valve. There was a spaded extension in line.

After changing the thermostat, pilot generator, banging on the valve to make sure it wasn't jammed, vacuuming... finally called in a pro who found the loose connect after about 10 min of poking around.

Worth the $60 to resolve the frustration. Plus no new hardware needed so I can return all the part I bought. Stupid noob mistake...
 
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Old 10-26-07, 06:57 AM
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Originally Posted by DoAsFan View Post
Thanks all for all your suggestions.

Turns out it was a loose connection between the apparatus and the gas valve. There was a spaded extension in line.

After changing the thermostat, pilot generator, banging on the valve to make sure it wasn't jammed, vacuuming... finally called in a pro who found the loose connect after about 10 min of poking around.

Worth the $60 to resolve the frustration. Plus no new hardware needed so I can return all the part I bought. Stupid noob mistake...

It sounds like you made a wise decision. Glad to hear you're back up and running. Thanks for the feedback.
 
 

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