Quick Thermocouple Question

Victor_Wenzel

AO Smith Gas water heater. Millivolts measure constant 28mVDC w pilot lit. Burner runs, when it goes out, the pilot goes out. Took a time lapse. Doesn’t look like TC issue to me. First pic is “normal”. The 2nd pic you can see TC glowing and pilot out. 

Pipe

Measure MV disconnected from the GV.

109A_5

Hello @Victor_Wenzel,

Even though the thermocouple is being heated properly, it does not mean it functions properly. If you DIY it is probably the most inexpensive part you can change.

mattmia2

Does it go out because the t-stat is satisfied or is it just going out? flame arrestor water heaters have screens that get clogged and starve the burner of combustion air but that is if it goes out before satisfying the t-stat.

Larry Weingarten

Hi, Also check, clean and retighten the connection where the thermocouple screws into the gas valve. A tiny bit of corrosion there can mess things up.

Yours, Larry

Mad Dog_2

Intermittent pilot outages are THE most difficult problems to diagnose & fix. The guys are right. It would behoove you to get @Tim McElwain's opinions here too. He is the King 🤴 in this Particular Kingdom...oh Timmie....Mad Dog 🐕 

Victor_Wenzel

@Pipe, that’s what I did, and it stood solid at 28mV. @109A_5, already on the way. Gets here today. @mattmia2, I took the screens completely off for the test. @Larry, i removed, I did not clean. I will do that when I get home tonite. Thanks a ton you guys! I didn’t know I’d get so many responses so quickly!!

Alan (California Radiant) Forbes

I've seen the magnet in the control go bad.

Victor_Wenzel

@Alan (California Radiant) Forbes, is that in the GV? @Larry Weingarten, I tried cleaning the TC wear it screws in. Same result. 😢

Victor_Wenzel

New thermocouple assy…can anyone tell what would cause this?

mattmia2

What is the gas pressure when it is firing and when it goes out, on both sides of the valve?

Victor_Wenzel

@mattmia2, do I need a special tool for that?

mattmia2

you need a manometer or a length of tubing fashioned in to a monometer

109A_5

Hello @Victor_Wenzel,

Does that pilot flame end up in the wrong place after the main burner goes off ? So the thermocouple is no longer being heated. Does the gas tubing or the fitting for the pilot have a leak ?

Larry Weingarten

Hi, It looks like the gas valve is shutting off slowly, or is sticky. You shouldn't have the flame out of the main gas orifice as the last pictures show. There is a chance of carbon buildup in the burner and at the orifice. The orange flame could be a clue. I'd consider washing out the burner and removing/cleaning the orifice. This work needs to be done outside of the heater. Are you on natural gas or propane? Propane can soot up pretty easily if draft is impeded anywhere. Checking gas pressure as @mattmia2 suggested, will help in understanding what's really going on.

Yours, Larry

Victor_Wenzel

Thanks everyone! Turns out the screen under the burner needed to be super cleaned. Blew the hell out of it with compressed air. Started back up and it’s been going ever since. I didn’t know that existed. A buddy told me to try it. Again, you folks rock!!!