Barn Furnace won't fire. HELP

[TractorJeff]

PS
Static pressure of 11 inches isn't the same as flow pressure of 10 inches. There maybe a flow restriction in the line.
Also
I don't believe that is a copper thermocouple line but a pressure tube that senses flame/heat thus allowing the Gas valve to open. If it is damaged/crimped you may not be getting the "Its Safe to Flow Gas" signal the Gas valve requires!
For what its worth!
In my attic is an old early 80's vintage propane furnace re-jetted for natural gas. The Tech shows up to service the new TRANE downstairs. Looks at his work order sheet that says check and adjust gas pressure of upstairs furnace. He goes up there, sees the vintage, gets angry/salty. He insists you can't run a propane furnace on natural gas! I tell him I am sure it has been re-jetted in its lifetime or it would have failed by now. I threaten to call his Boss if he doesn't do as WO states. He knuckles under, checks it, adjusts a little as it was slightly low.
Moral of the story is;
GOOGLE is your friend! Ask for opinions and suggestions here! Study your Unit and compare to other old furnaces.
Not every Furnace Tech can handle OLD units!

 

[xtremek]

I hear you Sub, but so far, everything that was wrong was either missed by, or cost me big dollars for a stupid, but labor intensive job. I'll keep plugging away at it.

Tractor Jeff, thanks for the help. I'll be checking to see if my local HVAC supply house or Grainger have that part in stock and get it replaced. And I get the difference between static and dynamic pressure. And I think I'm a little low on static pressure, so I'm probably really low on dynamic.

 

[Travo131]

Sounds like your line is undersized going to the furnace. If you are only getting 9 inches at the 2nd stage pull the black cap off the regulator and turn it in 1 to 2 turns, that will raise the pressure.

 

[My Old Tools]

What size is your supply line? Even with more pressure it may not flow enough to keep up with the burners, hence the pilot going down.

 

[xtremek]

Sounds like your line is undersized going to the furnace. If you are only getting 9 inches at the 2nd stage pull the black cap off the regulator and turn it in 1 to 2 turns, that will raise the pressure.

What does the tool you adjust the valve look like?

What size is your supply line? Even with more pressure it may not flow enough to keep up with the burners, hence the pilot going down.

I went with 1/2" black pipe that the furnace came with.

 

[Travo131]

What does the tool you adjust the valve look like?



I went with 1/2" black pipe that the furnace came with.

A bigger flathead screwdriver. 1/2 inch pipe will do it. I would bump that thing up to min of 11 inches. the link should help you out a bit.

http://www.hvachowto.com/2014/11/16/test-water-column-gauges-gas-furnaces/

 

[FullRaceMerc]

It does sound like a gas flow issue. I don't normally work with LP, so my thoughts are more along theoretical lines related to natural gas experience, instead of direct LP knowledge.

Is it hard piped, or do you have a gas flex connector running to the heater? If it's flex, is the flex rated correctly for the size of the heater? Too small of a diameter or too much length can reduce the gas flow. A 3/4 flex can be rated over 200,000 BTU, while a 3/8 flex can be under 30,000 BTU. Typically there is a tag on a new flex line.

Have you looked at the inlet of the gas valve? Sometimes you will find crud blocking an inlet screen. It's probably more likely on a used unit that has been moved.

Ok, the valve has a yellow sticker on the side saying that it's "....been converted to run on LPG". The propane guys put a tee in after the red regulator on the tank with a ball shutoff valve. Then, where the line comes outside of the wall, they put a brown regulator. It then has a 10' run up the inside of the wall, a 30' run through the rafters and 2' drop down to the furnace. I've got a pic of the flames, they're small blue flames, about a 1/4" tall. As far as the orifices are concerned, they're more slots than holes and they were clogged, but I did clean them out completely. Before I cleaned them, the gas would build up in pockets until everything went BANG. Now, when I use the torch, it's a nice steady light off (fairly quick, but no big bang), so I'm pretty sure I got them clean. When I use the t-stat to try and fire the furnace, the pilot flames drop down severely. Again, I really appreciate EVERYONE's input.

You mentioned 1/2" gas pipe. This ^ looks like a 42' run after the regulator. Plus more calculated length for elbows. The chart linked below shows 1/2" pipe used for LP dropping BTUs quite a bit as you add length. Per the chart if it were only 40 feet of 1/2" it would only be rated for 129,000 BTU. At 50 feet it drops to 114,000 BTU. Your heater is shown as 180,000 BTU on the tag you posted. If it were 3/4" pipe it shows 185,000 BTU at 80 calculated feet. That sounds like plenty for your 42 feet plus several elbows. It is not uncommon in natural gas work to use a "Balloon Line", where the pipe size out of the regulator is stepped up to run a long distance before being reduced at the appliance. I would think the same would apply to LP.

www.endot.com/OpenFile.aspx?path=21eb7_0.pdf&Type=1&pid=34 Again, I don't normally work with LP. This is a chart found online, not one that I have experience using.



As for the earlier references to the orifices, those aren't the slots in the burners, but the little jets with the small holes that shoot gas into the burner. Drawings below. Those slots in the burners are important, but you should also check the orifices if you still have trouble after the gas flow to the unit is determined to be ok.

 

[xtremek]

It is hard piped all the way and there are two elbows and two tees for drip legs. I'll pull the line off at the valve to check the screen, and I'll check the orifice as well. I don't think its an orifice issue because I notice when the burners are signaled to light, the pilot flame drops to about half it's original size.

 

[D45]

Is the 40 feet of 1/2" line solely used for this heater?

or, does this 1/2" line supply LP to anything else?

 

[FullRaceMerc]

It is hard piped all the way and there are two elbows and two tees for drip legs. I'll pull the line off at the valve to check the screen, and I'll check the orifice as well. I don't think its an orifice issue because I notice when the burners are signaled to light, the pilot flame drops to about half it's original size.

All hard pipe, so no restrictions from flex. Check.

Agreed, the orifices seem less likely than other possibilities. It is a location that you would normally check, but with your pilot dropping at start-up it is probably earlier in the system.

I was running out of time yesterday & should have been clearer & moved the final thoughts to the bottom of the reply. I think your 1/2" pipe for the 42' plus fittings after the regulator is too small as per that chart I linked. According to the chart it looks like 3/4" would be the minimum size at your distance for a 180,000 BTU heater.

 

[naturalgas]

I'm willing to bet your whole problem is the pilot. You already cleaned out the burners so they are good. I think your pressure is ok. Disconnect the pilot line at gas valve and blow compressed air through it. You should see plenty of dust come out if your burners were that dirty. Get a new thermocouple and reconnect pilot line and new t-couple. Then light pilot leaving gas valve in pilot position and adjust pilot at valve. There is a screw cover on valve near pilot tubing for adjustment. Remove top screw cap and down lower is an adjustment screw. Clockwise will make pilot smaller and counter larger. Adjustment is very little from small to large so go easy you will see. When you have a good looking pilot turn valve to on position and check ignition. You may need a new pilot but a universal target pilot will work good for that application. Make sure when your cleaning and adjusting pilot the power is off to unit. And when you fire it up 1st try do it from thermostat. You don't want a free haircut eyebrows done. As others have said you-tube is your friend. It's really a simple fix.


Sent from my iPad using Tapatalk

 

[xtremek]

Yes, the 40' is strictly for this furnace. Given the model number, NAS100, which is easier to read, I'm wondering if it's only 100,000 btu's. I 'll check some of those things tomorrow. No chance to even look at it today. And I'll keep everyone in the loop on what I find. Thanks for your help.

 

[xtremek]

So I caved in and had the furnace guys (Chasco) back out. He checked the pressure static at the brown regulator and had 24" of water. Checking the dynamic pressure at the valve showed 1.3" of water. After 2 hours and trying a bunch of different things, we decided to pull the regulator off the outside of the barn and pull the line off just in front of the shutoff valve. I fired up the compressor, adapted fitting to go from my air nozzle to the 1/2" pipe sticking out of the barn and put 170+psi to the lines. Barely no air came out until there was a loud pop I could hear outside the barn, and then we had good flow. It ended up being a peanut sized chunk of pipe dope. Another blast to make sure everything was clear, button it back up, fire the furnace up, and it's been running fine since then. It sure is nice to be able to hear yourself think in the barn now. Thanks everyone for your help and suggestions.

 

[xtremek]

So I caved in and had the furnace guys (Chasco) back out. He checked the pressure static at the brown regulator and had 24" of water. Checking the dynamic pressure at the valve showed 1.3" of water. After 2 hours and trying a bunch of different things, we decided to pull the regulator off the outside of the barn and pull the line off just in front of the shutoff valve. I fired up the compressor, adapted fittings to go from my air nozzle to the 1/2" pipe sticking out of the barn and put 170+psi to the lines. Barely no air came out until there was a loud pop I could hear outside the barn, and then we had good flow. It ended up being a peanut sized chunk of pipe dope. Another blast to make sure everything was clear, button it back up, fire the furnace up, and it's been running fine since then. It sure is nice to be able to hear yourself think in the barn now. Thanks everyone for your help and suggestions.

 

[D45]

Good deal, glad it was something somewhat simple, yet nerve racking

 

[isb cornbinder]

My first trade was a Sheetmetal Mechanic. I did HVAC for more than a few years. I am thinking your situation is the pilot light being too far away from the burner. A plugged orifice nearest to the pilot may cause poor ignition and back-firing, The pilot should be close to and just slightly below the centre line of the burner. Try to line the pilot with one burner orifice.
If this furnace is used, and was not protected, there could be "stuff" in the burner pipe.
I doubt air in the lines is your problem because the pilot continues to operate.
If the furnace is in a draft the air movement can blow the gas away from the pilot until the random gas build up catches on fire with a boom. Make sure your system has a chimney cap to control the draft up the chimney. Try to guard the burner box from cross breeze.

 

[xtremek]

isb, the pilot light was part of my initial problem, along with plugged burners. I used it for several TROUBLE FREE hours last night. Here's a picture of the offending pipe dope. Thanks again for everyone's suggestions and help.

 

[gungatim]

AWESOME!!!

see, you don't have to run out and buy new, just understand how it works, check and verify the basics, and use good troubleshooting techniques and you'll win nearly every time...

 

[xtremek]

AWESOME!!!

see, you don't have to run out and buy new, just understand how it works, check and verify the basics, and use good troubleshooting techniques and you'll win nearly every time...

Preach that!!!! In the end, it would have still cost me the same amount of money, as all of the issues I had to pay for were due to my installation techniques. It did cost me several hours of work to fix the old beast, but that's cheap compared to the $1500+ for a new furnace. Score a big one for the cheapstake.

 

[gungatim]

Preach that!!!! In the end, it would have still cost me the same amount of money, as all of the issues I had to pay for were due to my installation techniques. It did cost me several hours of work to fix the old beast, but that's cheap compared to the $1500+ for a new furnace. Score a big one for the cheapstake.

yeah but you didn't just pay for the fix, you bought an education. skills and experience are better than just going the easy route any day in my book...

 

[sublime68charger]

Glad it's working now for you!

Though I did call the swallow your pride and call in a expert as my only non expert advice!

Happy new year nice and warm now!

 

[xtremek]

You called it, Sub. It wasn't so much swallowing my pride as it was opening my wallet. It takes a lot to get it open sometimes.

 

[sublime68charger]

you just need to get out the pry bars and the big hammer and once you get the rust knocked off and shine in there with a Big Ol Flood light you might find some Money way down in the depths under all the other bills and recipients that are in there! LOL!!!