Furnace thermocouple problem

[California]

must be on a natural draft furnace, and not a vent motor assist type. Does the B vent run up through the interior of the house and exit the roof, or does it go through an outside wall, and run up the outside wall of the home ?

The latter. I just now looked in old photos that I made after we took over the ranch in Y2K.

'Cozy' space heater, if you're familiar with them. It's all we need for this 700 sq ft simple farmhouse. Our home in town is normal but everything at the ranch is farmer-designed/installed with no regard for code.

That's about 3 ft horizontal.

And (old photo below) the exterior stovepipe, as it was back then.

The pro took one look at that, said 'There's your problem!'. Then he added an offset, that extends above the roof.
No problems since.

Occasionally its worth what it costs to get someone in who knows what he's doing. I never would have thought that was why the vent safety device was tripping - because it needed a taller vent.

 

[California]

Thanks for the update.

Just to make you feel better, you were 17+ years younger when you posted that originally.

Thanks for reminding me? I've reached the age where I prefer to ignore birthdays.

 

[MossRoad]

But that's the day I get German Chocolate cake!

 

[SandburRanch]

Hey California , thanks for the update . Those old posts can often remind us that things changed dramatically when the foreign market took charge and buying new often doesn't solve the problem because we've just bought another foreign market product .

And another reminder for us , you keeping the manual to check the information there is a + , even though it may be a decade later when read . We have a Cozy wall heater that was installed new in 1983 before the foreign market took complete control of our lives . The Cozy wall unit has preformed flawlessly albiet it's used less than our central hvac unit .

For those young whipper snappers that may not know there are thermocouples and thermopiles ,
the thermopile does not need purchased elect. power to operate the thermostat because it generates its own current . Wikipedia explains that well . Being we have a propane supply , it's saved our butts several times in nearly 40 years when ice storms knocked power out for a week at a time . You might do a little investigation to determine if your stove can be changed to thermopile if you would like heat when elect. power fails .

 

[gasman1075]

Hey California , thanks for the update . Those old posts can often remind us that things changed dramatically when the foreign market took charge and buying new often doesn't solve the problem because we've just bought another foreign market product .

And another reminder for us , you keeping the manual to check the information there is a + , even though it may be a decade later when read . We have a Cozy wall heater that was installed new in 1983 before the foreign market took complete control of our lives . The Cozy wall unit has preformed flawlessly albiet it's used less than our central hvac unit .

For those young whipper snappers that may not know there are thermocouples and thermopiles ,
the thermopile does not need purchased elect. power to operate the thermostat because it generates its own current . Wikipedia explains that well . Being we have a propane supply , it's saved our butts several times in nearly 40 years when ice storms knocked power out for a week at a time . You might do a little investigation to determine if your stove can be changed to thermopile if you would like heat when elect. power fails .

You would need to replace the pilot assembly, gas valve and thermostat as well.

 

[California]

You would need to replace the pilot assembly, gas valve and thermostat as well.

Yes, you would need a different gas valve (~$150) that accepts a thermopile.

I'll add here a couple more things I have learned since that first inquiry in 2004:

The ranch guest cabin had a simple through-the-wall heater. Its flame chamber cracked open before it was 10 years old. I bought a replacement, Empire brand, from Northern Tool. No electrical connection (except for its optional fan) because it uses a thermopile to power its gas valve.

Generic picture.

After a few months in use this replacement heater wouldn't respond to the wall thermostat. I measured the millivolts from the thermopile and found a voltage loss at the new Honeywell wall thermostat which has mechanical points. So I replaced the thermostat with an Empire mercury-filled wall thermostat. No improvement, the mv reading remained at what Empire specified as minimum acceptable. Replaced the thermopile. Slight improvement in measured mv but it still failed to come on reliably as the thermostat called for heat.

Ok, if the nearly new thermopile then its new replacement weren't making enough voltage there was only one thing left to do. I took the burner assembly apart and bent the shield over the pilot light to direct more flame onto the thermopile. Success!

Generic photo - with the shield correctly aimed.

And a similar pearl of wisdom to share: I discovered the gas clothes dryer has a flue overheat sensor similar to the furnace - but with different appearance. Replacing that, under $10, was all it took to get the clothes dryer back in service. This saved the minimum $100 for a service call to have a pro repair it.

 

[kenmac]

The latter. I just now looked in old photos that I made after we took over the ranch in Y2K.

'Cozy' space heater, if you're familiar with them. It's all we need for this 700 sq ft simple farmhouse. Our home in town is normal but everything at the ranch is farmer-designed/installed with no regard for code.

That's about 3 ft horizontal.

View attachment 735273

And (old photo below) the exterior stovepipe, as it was back then.

The pro took one look at that, said 'There's your problem!'. Then he added an offset, that extends above the roof.
No problems since.

Occasionally its worth what it costs to get someone in who knows what he's doing. I never would have thought that was why the vent safety device was tripping - because it needed a taller vent.

View attachment 735271

Brand really doesn't matter. Down here we call them circulator heaters. Usually, you would go up off the back of the heater to establish draft. Yours off the draft diverter with 2 90 deg. ells which in it's self can cause problems.

But that ''pro'' is correct, that vent should go above the roof, but I have seen them operate just fine like your's is vented

Is that heater also a MV system ? If so, It should put out around 750 MV with a good strong flame. The issue with the MV system is, it doesn't take much resistance within the circuit to kill your MV to the gas valve. Loose connections, corrosion, etc,. Even a incorrect T. stat can rob MV the GV gas valve needs to operate.

At one time, all the old homes had a floor furnace with these MV systems

 

[California]

Is that heater also a MV system ? If so, It should put out around 750 MV with a good strong flame. The issue with the MV system is, it doesn't take much resistance within the circuit to kill your MV to the gas valve. Loose connections, corrosion, etc,. Even a incorrect T. stat can rob MV the GV gas valve needs to operate.

At one time, all the old homes had a floor furnace with these MV systems

Yes, both this heater in the farmhouse and the one in the cabin have thermopiles and work fine when the power is out. The house heater has been flawless after its chimney was extended upward and its flue overheat sensor maintained, connections cleaned occasionally.

I don't remember the mv reading for that troublesome cabin heater but maybe from memory, 400 mv then 175 after its wall thermostat called for heat. Bending the flame guide above its pilot to put more flame on the thermopile brought the thermopile up to spec, I think it was 750 mv or more. No problem since. But that was a frustration maker, a manufacturing defect, with only the tip of the thermopile heated before I reshaped the flame guide. I had called Empire's advice tech and his only recommendation was replace the gas valve which would have been a costly mistake.

Our real home 100 miles away in town, built 1940, still has the original two floor furnaces that have been flawless for the 40+ years we have lived there. No electrical connections so they must have thermopiles too. When I built a second story onto that house in 1988 we put a modern heat pump in the upstairs but nearly never run it. The floor heaters downstairs warm the entire house. If we come home to a cold house after some time at the ranch and the weather is below 50 degrees we might run the heat pump for the first 2 hours. Its only real use is summer air conditioning.

 

[gasman1075]

Yes, both this heater in the farmhouse and the one in the cabin have thermopiles and work fine when the power is out. The house heater has been flawless after its chimney was extended upward and its flue overheat sensor maintained, connections cleaned occasionally.

I don't remember the mv reading for that troublesome cabin heater but maybe from memory, 400 mv then 175 after its wall thermostat called for heat. Bending the flame guide above its pilot to put more flame on the thermopile brought the thermopile up to spec, I think it was 750 mv or more. No problem since. But that was a frustration maker, a manufacturing defect, with only the tip of the thermopile heated before I reshaped the flame guide. I had called Empire's advice tech and his only recommendation was replace the gas valve which would have been a costly mistake.

Our real home 100 miles away in town, built 1940, still has the original two floor furnaces that have been flawless for the 40+ years we have lived there. No electrical connections so they must have thermopiles too. When I built a second story onto that house in 1988 we put a modern heat pump in the upstairs but nearly never run it. The floor heaters downstairs warm the entire house. If we come home to a cold house after some time at the ranch and the weather is below 50 degrees we might run the heat pump for the first 2 hours. Its only real use is summer air conditioning.

Empire floor furnaces are very reliable but make sure the vent pipe is maintained and inspected regularly. And that the redundant high limit has been installed as well ( yellow wire to a high limit) depending on the year they would have 2 high limit switches right from the factory. Although reliable they are not very efficient. IMO

 

[kenmac]

Yes, both this heater in the farmhouse and the one in the cabin have thermopiles and work fine when the power is out. The house heater has been flawless after its chimney was extended upward and its flue overheat sensor maintained, connections cleaned occasionally.

I don't remember the mv reading for that troublesome cabin heater but maybe from memory, 400 mv then 175 after its wall thermostat called for heat. Bending the flame guide above its pilot to put more flame on the thermopile brought the thermopile up to spec, I think it was 750 mv or more. No problem since. But that was a frustration maker, a manufacturing defect, with only the tip of the thermopile heated before I reshaped the flame guide. I had called Empire's advice tech and his only recommendation was replace the gas valve which would have been a costly mistake.

Our real home 100 miles away in town, built 1940, still has the original two floor furnaces that have been flawless for the 40+ years we have lived there. No electrical connections so they must have thermopiles too. When I built a second story onto that house in 1988 we put a modern heat pump in the upstairs but nearly never run it. The floor heaters downstairs warm the entire house. If we come home to a cold house after some time at the ranch and the weather is below 50 degrees we might run the heat pump for the first 2 hours. Its only real use is summer air conditioning.

I really hate to try to diagnose an issue over the phone. there can be so many things.
Had a guy call today about a gas valve on an RV refrigerator. He was wanting to be able to trouble shoot the GV over the phone. I told him I would just need to come check it out.

I have crawled under thousands of homes and worked on those old floor furnaces.
I would be very surprised to find any in my area these days .
I changed out my share of those things back in the day in favor of central heat/ air.

Those old MV systems are/were pretty basic systems compared to these systems we have today !