Teledyne Laars Series 2, 3rd Thermopile in 2 seasons ??

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MJCP

MJCP

0
Sep 14, 2007
139
Michigan
original symptom - Pilot stays lit, heater will not turn on
While troubleshooting I would use a jumper to bypass the various switches looking for a bad switch.
The heater would come on eventually, but never while bypassing the same switch.
I suspected the thermopile was not getting enough voltage to turn on the gas valve.
I cleaned the pilot tube and orifice to make sure I had a good pilot flame - no change.
Took voltage readings on thermopile, expected 500-700 mV, only had 100-200.
Bought a new thermopile - better voltage readings 300-500 still heater would not come on without a random use of jumpers.
I assumed that the use of the jumper was creating a "spark" like jump in the millivolt range that would be enough to turn on the gas valve. As long as the heater turned on when I needed it I figured I could live with it for the rest of the season.

New season couldn't get that Lucky Spark - decided to spring for a new gas valve..... NOPE...
Maybe I got a bad Thermopile??? Bought a new thermopile ... Success!!!!!! For 3 months.....
Today the heater shut off and the pilot went out, I relit the pilot but it will not stay lit

What are the chances its another bad thermopile?
Is there something else that can be causing the thermopile to go bad?
or am I missing some other possible cause?

Any ideas are appreciated, I'm about to buy another thermopile, but I think I'm missing the real problem here.
Thanks in advance for any help
 
Here is what I would do, replace the unit and be done with it. Obviously you could be chasing an issue forever and replacing bits and pieces of the unit. Add in the frustration factor of trying to figure out whats wrong with the heater and at some point you have to decide if it's worth the frustration and aggravation. Fix a part today, next week it's something else or maybe the same part.

If the pilot won't stay lit you have either a bad thermopile, gas valve, or a short somewhere. The thermopile has to generate enough milivolts so that when you release the gas valve knob in pilot mode, it activates a selenoid in the gas valve to keep the pilot portion of the valve open. If this doesn't happen, the pilot goes out. If you have a short in one or more of the safeties then it's draining down your millivolts and causing your issue. Have you taken any new millivolt readings on the thermopile? You can hook your volt meter up to the pilot leads, turn the gas valve knob to pilot, light the pilot and keep the knob in pilot mode and get your millivolt reading. If you get 400+ mv, then the thermopile is good and now you need to start looking elsewhere, maybe a short.

I know it's hard to come to the conclusion of a new unit is needed and the price is hard to swallow but consider the age of your existing unit and again your aggravation. Not to mention you are dealing with a millivolt system which by today's standards is archaic.
 
How well immersed in the pilot flame is the powerpile? A weak pilot can cause a low millivolt reading. Also, any corrosion on connections can cause enough resistance to lower the millivolts getting to the gas valve
 
took readings today and found that I only had 33 mV after holding the pilot for several minutes, it slowly kept climbing .1 every few seconds but clearly not acceptable. I ordered a new thermopile, and will install it next week. At that time I will again check the orifice, and the position of it in the pilot flame. Since it was working fine until the middle of the day yesterday, I assume it was a failure of the device. I am now curious what would cause this premature failure. I can only think that the position of the device could be a factor, but it fits into a sturdy assembly, clicks into place, and there isn't really any adjustment. I guess I could be getting bad devices but I doubt that too. I could try to eliminate the possibility of shorts by temporarily bypassing the safety switches, but I'll leave that for next week also. I'm still open to any ideas of what could cause the failure so feel free to weigh in.
 
Flame strength. If the flame isn't strong enough it will not heat the thermopile correctly. Take the thermopile out and hold a lighter to it while measuring the mv.
 
When the repair guys did my heater this spring- they put in a new gas valve and the entire pilot light assembly, which is the one burner row, new pilot, and thermopile. He said that fixes almost all the issues and if it's anything more than that, he recommends buying a new heater. I did have a leaking/bad pressure valve which they switched too. So my non-expert opinion? Replace the pilot assembly and if that doesn't do it, get a new heater.
 
zimm said:
When the repair guys did my heater this spring- they put in a new gas valve and the entire pilot light assembly, which is the one burner row, new pilot, and thermopile. He said that fixes almost all the issues and if it's anything more than that, he recommends buying a new heater. I did have a leaking/bad pressure valve which they switched too. So my non-expert opinion? Replace the pilot assembly and if that doesn't do it, get a new heater.
Click to expand...

I would be currious to know what the symptoms were that prompted him to replace all of those parts. I have been working on heating systems for over 35 years now and can only recall having to replace an entire pilot assembly maybe 2 times.
 
ps0303 said:
Flame strength. If the flame isn't strong enough it will not heat the thermopile correctly. Take the thermopile out and hold a lighter to it while measuring the mv.
Click to expand...
That would be my guess as well. Probably a bit of corrosion in the orifice blocking the gas flow. I wonder if the OP can get a picture of the pilot burning?
 
I would be currious to know what the symptoms were that prompted him to replace all of those parts. I have been working on heating systems for over 35 years now and can only recall having to replace an entire pilot assembly maybe 2 times.[/quote]

Pilot light rusted out, wire broken, gas valve corroded shut, gas line to pilot was solid with corrosion, pressure switch was leaking and didn't work.... I have some pictures I can post if you'd like.
 
zimm said:
Pilot light rusted out, wire broken, gas valve corroded shut, gas line to pilot was solid with corrosion, pressure switch was leaking and didn't work.... I have some pictures I can post if you'd like.
Click to expand...
Wow, sounds prety nasty. Never seen that much damage in a heater. Keep in mind that I do house boilers at about a 20-1 ratio to pool heaters.

Unit should be in good shape for a few years now as most all of it has been replaced
 

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zimm said:
Oh, and the burners were buried under 4" of dirt because the backyard was draining past the heater and would flood out. Sorry to the original poster for going off-track. Hope you get it fixed!
Click to expand...

At that point I would have replaced the heater. That bill couldn't have been very cheap. And when you consider the age of the unit it probably would have been a better investment.
 
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