Oh Great and Wise HVAC Gurus

[Scout26]

Yep, the furnace crapped out last night.

Pilot light is lit
Fuses and circuit breakers are on, so there is power
Thermostat shows it's trying to fire it up

Beyond that I'm lost.

It's an American Standard
Model# TUP120B936A0
Serial# E29630504
MFD: 7/90  (Yes, it's 25 years old, but if possible I'd rather not replace it just now.)

Any help would be appreciated. 

[Nick1911]

Any fans running?  Other noises?

[TechMan]

We had the same issue and my FIL came down and found that one of the pressure sensors had gone bad.  Replaced it and it was working fine.

[Nick1911]

We had the same issue and my FIL came down and found that one of the pressure sensors had gone bad.  Replaced it and it was working fine.

Unfortunitly, I don't think scout's furnace has a pressure sensor.  It's a Category I furnace - natural draft.

Personally, I'd start by jumping R to W on the furnaces circuit board.  That will eliminate the thermostat as a potential culprit. 

Beyond that, it's hopscotching through the wiring with the wiring diagram and a multimeter.  Possiably a control transformer, gas valve, or fusiable link somewhere that's opened.

[Brad Johnson]

Any fans running?  Other noises?

This.

Also, does that model have a flame sensor for the main burner?

Brad

[Scout26]

Any fans running?  Other noises?

No, but Ron called me and offered to come out and take a look.  I forgot he did HVAC.  (Along with how many HVAC experts we have on here.)


I love this place.  

[TechMan]

Unfortunitly, I don't think scout's furnace has a pressure sensor.  It's a Category I furnace - natural draft.

Personally, I'd start by jumping R to W on the furnaces circuit board.  That will eliminate the thermostat as a potential culprit. 

Beyond that, it's hopscotching through the wiring with the wiring diagram and a multimeter.  Possiably a control transformer, gas valve, or fusiable link somewhere that's opened.

Shows you how much I know about HVAC.   

[RocketMan]

Your furnace is broken, Scout.  Once you fix it, it will work again.  Where do you want me to send the bill? 

[wmenorr67]

Just caveman it and build a fire.

[Scout26]

Your furnace is broken, Scout.  Once you fix it, it will work again.  Where do you want me to send the bill? 

Ha !!!   Sorry, but no can fix.  Need to replace.  Ron came out and quickly diagnosed the problem, which we thought would be about a $60 part.  Turns out I have a unicorn, so the part would have been $250.  I was willing to put $60 into a 25 year old furnace, but not $250.  So he hooked me up with a friend of his to install a new 90% furnace. 

Just caveman it and build a fire.

Yep, first thing yesterday morning, got the fireplace going along with breaking out a couple of the space heaters from the camper.   SO yes, we were "camping" in our own house last night.

[K Frame]

What's a 90% furnace going to do to your venting situation? I don't think you can use the chimney to vent at 90% efficiency, as the flue gases are too cool. And you have to worry about the flue gases, or you'll become a (formerly) living example of my signature.

[Scout26]

He's going to run two PVC lines out the back wall.  One for intake and one for the exhaust gases.

[Brad Johnson]

Hot exhaust gasses and PVC es no bueño.

Brad

[Ron]

Hot exhaust gasses and PVC es no bueño.

Brad

What heat?

[Nick1911]

Hot exhaust gasses and PVC es no bueño.

Brad

...It's a well accepted practice for condensing furnaces.  The flue gasses are leaving the unit at luke warm temperature.

For instance, here's what the installation manual from equipment I install has to say on the matter:

All combustion air and vent pipe must conform to American National Standards Institute (ANSI) and American Society for Test-ing and Materials (ASTM) standards D1785 (Schedule 40 PVC), D2665 (PVC-DWV), F891 (PVC-DWV Cellular Core), D2261 (ABS-DWV) or F628 (Schedule 40 ABS).

[Brad Johnson]

...It's a well accepted practice for condensing furnaces.  The flue gasses are leaving the unit at luke warm temperature.

Ah, gotcha.

Brad

[K Frame]

Hot exhaust gasses and PVC es no bueño.

Brad

At 90% efficiency and above the exhaust gases are cool enough that standard PVC is the vent material of choice.

[Ron]

PVC is impervious to the corrosive effects of any byproducts of combustion.

The cross referenced gas valve by the same manufacturer (White Rogers) was the $250 (cost) valve.

I had them look for a Honeywell equivalent and his valve has no Honeywell valve that is recommended as a replacement.

[K Frame]

What, he's too frigging lazy to walk down into the basement and turn the gas on and off when he wants heat?

[Scout26]

What, he's too frigging lazy to walk down into the basement and turn the gas on and off when he wants heat?

I can turn the gas on and off all I want, but without the valve assembly the furnace won't work. 

New furnace is actually going to be 2 stage, 96% efficient.  The "exhaust gases" consist many of luke warm water vapor, CO and acidic/corrosive byproducts that would eat the existing chimney liner, so it'll be vented out the back wall.  (There will also be an air intake PVC line also).

So both my natural gas and electric bill should drop fairly substantially.   

[K Frame]

"I can turn the gas on and off all I want, but without the valve assembly the furnace won't work."

You bypass the gas valve with a piece of bendy straw and use one of these!



Little duct tape to seal the ends and you're good to go.

DUH!

[K Frame]

Acidic discharge water isn't the word for it. How are you going to dispose of it? Most of these furnaces won't fully exhaust the combustion by products and you have to deal with essentially battery acid water that has to be pumped somewhere.

A lot of municipal systems are placing restrictions on untreated furnace discharge because it can be so acidic. Don't even think about running it into your septic tank if you have one of those.

[never_retreat]

[Scout26]

Acidic discharge water isn't the word for it. How are you going to dispose of it? Most of these furnaces won't fully exhaust the combustion by products and you have to deal with essentially battery acid water that has to be pumped somewhere.

A lot of municipal systems are placing restrictions on untreated furnace discharge because it can be so acidic. Don't even think about running it into your septic tank if you have one of those.

It's in the luke warm water vapor, so it goes into the atmosphere where it combines with the burnt byproducts of floppy disks to create poison rain in NOVA.

[Scout26]

As an update:

New furnace will be installed tomorrow.  In the meantime, we've been running two mini-spaceheaters in the main part of the house (with one being moved into the bedroom at night (yes, he's moved in with me during the "crisis") , a third one is in a closed off back bedroom with my dialysis supplies since the boxes clearly state "Not to be stored below 60F"

With just the two space heaters and the fireplace we managed to raise the temp in here from 60F Tuesday morning to 63F this morning to 69F this evening.

I'm going to hate to see my electric bill.