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Rick
Rick, HVAC Supervisor
Category: HVAC
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Experience:  40+ yrs. experience as a licensed oil & gas technician.
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gcv40-100 a. o. smith water heater, cleaned thermo couple

Resolved Question:

gcv40-100 a. o. smith water heater, cleaned thermo couple and burner, lights easily and gets water to temp then it will go out. Pilot light is hitting thermocoulple ??
Submitted: 4 years ago.
Category: HVAC
Expert:  Rick replied 4 years ago.

Rickheatdoc :

Welcome to Just Answer, I will do my best to help you with your problem

Rickheatdoc :

Does your heater have a sealed combustion chamber?

Customer:

yes

Customer:

2005 model

Rickheatdoc :

Then the air intake vents are probably clogged up. When this happens turbulence is created when the main burner shuts down putting out the pilot

Customer:

how much clogging does this take to cause this?

Rickheatdoc :

That's impossible to quantify

Rickheatdoc :

Is there a screen around the base of the heater?

Customer:

yes, and it did have some lint on it.

Rickheatdoc :

try cleaning the screen and remove it and vacuum under the heater if you can

Customer:

I did start the pilot and let it burn for about a minute before i turned the burner on and it stayed lit so that is why i thought the thermocouple was ok..would that make sense

Rickheatdoc :

Given it's age the thermo could be weak. You would need to put a meter on it to read it's volatage output to be sure. Could also be a weak pilot flame

Customer:

I will clean screen if that doesnt work i think that i would have to replace the whole burner assambly because the thermocouple assambly is soldered in and it has a "resistor looking thing" in line and does not look like a traditional replacement thermocoupler.

Rickheatdoc :

Not sure which version you have but some are more involved than a standard thermocouple. I would put a meter on it first to be sure. You should read 15 to 20 DC mV if it's good. A little less is OK given the very low voltage an the poor test connections. One lead goes on the copper wire the other on the tip that connects to the gas valve. You need to hold down the button to keep the pilot lit. It's a bit of a juggling act

Rickheatdoc :

a negative reading just means you have the leads crossed but it's still valid

Rickheatdoc :

If you pull the burner you should also vacuum inside the chamber

Customer:

already vacuumed the inside, would it matter that this house sat for 9 months with no occupants, would that make the thermo weak?

Rickheatdoc :

probably not

Rickheatdoc :

do you have any more questions?

Customer:

I dont have my meter here so i am going to just clean it and see what happens for now... thank you

Rickheatdoc :

You're welcome
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