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P B G 11-03-2012 01:58 PM

Heater Problems!
 
Talk to me HVAC guys.

I have a Modine 100000 BTU heater, ductless in my shop.

The standing pilot won't stay lit. Getting 27.2 millivolt at the thermocouple when I hold the red button in and relight my heater.

Getting ~28 volts at the gas valve when I turn the thermostat up, thus indicating the safety switches are not tripped (they are in series with the gas valve on the wiring diagram).

What else is there that could be bad? I tried a new thermocouple for 11$ sh1tz and giggles, no go, which I suspected would be the case with the reading I got.

I don't want to spend a couple hundred on a gas valve if I do not have to, but what else could it be?

D.T. 11-03-2012 03:50 PM

I'd probably put up model number and how old it is.

Try a propane torch and get the thermocouple red hot yet? Correct thermocouple? Tried the old one again? Clean it with emery cloth.

Gas valve issue is next.

P B G 11-03-2012 04:01 PM

Sure did use a propane torch, that was my first instinct.

Heater is a Modine PD 100AA0111 - Age is unknown, building is ~30 years old, but unknown who/when it was installed.
Red hot, pilot lit, release button - gas turns off.

Voltage at gas valve like that goes well above 30 during propane heating.

Thermocouple seems correct, it is appropriate for the gas valve mfg. Not a OEM product, but still I think an appropriate thermocouple replacement.

Swapped back to the original one anyhow, as I think it is a higher quality product, and generates good numbers on the meter.

D.T. 11-03-2012 04:09 PM

Pilot won't stay lit or main gas valve will not open?

One of these?

http://www.modinehvac.com/v2portal/p...ntent2_008.htm

P B G 11-03-2012 04:12 PM

Quote:

Originally Posted by D.T. (Post 19962978)
Pilot won't stay lit or main gas valve will not open?

One of these?

http://www.modinehvac.com/v2portal/p...ntent2_008.htm

Yup that's it.

The pilot won't stay lit, I have not attempted to light the main heater with out the pilot, as it is mounted ~20 feet in the air.

Is there a way to easily bypass the pilot needing to be lit in order to open main gas valve?

D.T. 11-03-2012 04:21 PM

Man, I hope not. :lol3

I need more info, like a wiring diagram and specs. Poor connection at the thermocouple/gas valve (the cold end)?

P B G 11-03-2012 04:33 PM

Connection seems good, it un-threaded smoothly by hand after cracking the threads loose. No signs of corrosion in the area/gunk in the threads, its not a gas connection after all.

http://i45.tinypic.com/dy4qb.jpg

D.T. 11-03-2012 04:38 PM

Gas valve issue. Pilot light should light and stay lit with no power at all (standing pilot I think).

Model # of the gas valve? Not sure the specs of the mV range for the gas valve.

Geez, now you made me tear apart my water heater and clean the thermocouple even though it works fine. :)

P B G 11-03-2012 04:47 PM

That was my understanding of these units as well, if you had the right MV at the thermocouple, that it should stay lit.

With how stupid expensive gas valves are I may just go away from a standing pilot, which just annoys me during the summer.

Beezer 11-04-2012 12:25 AM

a Modine that old prolly has cracks in the heat exchanger anyway. I would spring for a new HotDog before spending too much on repairs for that dinosaur. sorry.... but been there & done that

D.T. 11-04-2012 05:33 AM

I use a sunflower propane in my garage. Of course I have a CO detector in the garage also. Never makes it go up.

If the HE was cracked...:huh

Gas valves are cheap on flebay.

jbhawley 11-04-2012 06:15 AM

Quote:

Originally Posted by P B G (Post 19962996)
The pilot won't stay lit, I have not attempted to light the main heater with out the pilot, as it is mounted ~20 feet in the air. Is there a way to easily bypass the pilot needing to be lit in order to open main gas valve?

Hold the pilot button on the valve and propane torch heat up the thermocouple for a few seconds. This fools the valve into thinking the pilot/thermocouple is on. Then turn the valve to on position and torch light the burners. You should hear the gas coming into the main burners. If this happens adn the main burners light up properly, just let it burn until...usually the thermocouple will cool down (since the pilot is not on) and the heater will shut down.

If you cannot get the heater to light up in the manner then you either have a safety switch tripped or a bad valve.

Also, check to make sure that when you turn the valve knob from off > pilot > on that the underneath valve is turning and the plastic knob is not stripped/broken and just free spinning. I have seen this happen all too often with old heaters.

rebake 11-04-2012 06:27 PM

Blow out the pilot assembly with compressed air,the kind used to clean computers.Anything as small as a spider egg can restrict them enough to not work.Valve diaphram could be bad also.Ed

Bronco638 11-05-2012 07:39 AM

Quote:

Originally Posted by rebake
Blow out the pilot assembly with compressed air, the kind used to clean computers. Anything as small as a spider egg can restrict them enough to not work...

+1 on this but it sounds like the gas valve might be bad.

P B G 11-05-2012 07:38 PM

So my shop has 2 heaters!

The one referenced in this thread I haven't tried the air yet - but I do think we're dealing with a gas valve issue.

My second heater is also acting up, I suspect it has an issue with plugging in the gas line, as it has a rather yellow flame, although judging from the rust up under the heater, I think it is the OEM one with the shop.

So I am almost thinking of installing two new heaters.


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