# Gas water heater help



## Letterrip (Jul 28, 2013)

Went to a house today with an AO Smith 40 gallon natural gas water heater. Model GCV 40 100. Manufactured 2006. Has the sealed combustion chamber. No hot water. Pilot light is out. Lit the pilot figuring the thermocoupler will be bad. Pilot light stays lit. Give it a minute and adjust the temperature to start it heating. After about 10-15 seconds, the flame dies. Can't relight the pilot for a few. Not completely sure why I can't relight. I am assuming a built in safety. Repeat the process once it allows me to, letting the pilot burn for at least 5 minutes, and same results. To add to the history, one of our guys replaced the entire burner assembly in jan. 2012 (Which includes a new thermocoupler). Could it be the control valve? Intake screen is clear and vent appears open. I even pulled the cap off the vent to make sure it wasn't plugged. 

Not a tremendous amount of gas heaters here. Electric are by far the most common, so I only work on gas heaters every month or two. What is the deal with the thermocoupler. It has something that looks like a fuse in the lead going back to the controls. Always found that the universals would work before the sealed combustion chamber. These are a new animal. I hate being a simple parts changer and would like to solve the problem for the customer. What would be the proper proceedure for testing the control valve?


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## PlungerJockey (Feb 19, 2010)

Would you be willling to bet your life that the inside lower intake screen is clean.

In my opinion the AO Smith is the hardest to clean. I remove the front cover and pilot assembly. I then blow compressed air thru the air inlet screen to clean it and get all the dust out.

It is possible you have a weak thermocouple or the little watch battery lookin limit has a bad solder connection.

It sounds like it's dirty. Watch your flame does it stay blue? Right before it goes out does it look like the flame is yellow and dancing.

If the flame is good it's either a bad limit or a gas valve.


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## Letterrip (Jul 28, 2013)

Erm......inside screen?? Only noted the plastic screen on the outside. Like I say, not very prevalent here. But the flames stayed blue the entire time. No yellows or oranges. That's why I am leaning towards a gas supply issue such as the control valve prematurely shutting off, or the Thermocoupler. Just don't understand why the pilot would stay lit for a good 5+ minutes if the thermocoupler is bad.


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## PlungerJockey (Feb 19, 2010)

If you pull the pilot assembly cover and take a look inside. You will see a sheet metal pan with approximately a 5 inch hole. If you shine a light into the hole you will see the ceramic air inlet. It kinda resembles a honey comb pattern and has tiny holes. I've tried brushes and everything else but the best way to clean it is to use a compressor or air tank and blow it out. 

The thermocouple on the AO Smith's is a special animal. If you examine it you will notice the limit spliced into the center. If the temp on the burner chamber is excessive from flammable vapor, improper venting or being dirty it will melt the limit rendering the thermocouple useless.

I've seen several of these thermocouples that look fine and work fine till they get hot. The solder between the limit and the thermocouple is pretty fragile. They can get a crack in that joint. Everything will be fine till the burner chamber heats up and things start expanding. Once the gap in the solder expands and open the crack it weakens the single to the gas valve and shuts the unit down.

It very well could be the gas valve. I don't replace the gas valves on these heaters. They are a poor design. I tell the customer to put that 400 dollars towards a Rheem or Bradford White. I wouldn't replace just the gas valve anyway. I would throw a new pilot assembly in as well. Then they will be dealing with the same problems in a couple years, if their home is dusty or the tank may fail.


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## Letterrip (Jul 28, 2013)

So you like Bradford white? 20 years ago, Rheem and A.O. Smith seemed to last so much longer that I considered them a second tier manufacturer. Several here have mentioned them and I have a supplier trying to get me to buy BW from him. 

I tried calling tech support for some answers, but they want me on the job site during the call. I'll let you know how that turns out tomorrow.


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## PlungerJockey (Feb 19, 2010)

Rheem/Rudd are my favorite.

The Rheem family including the GE water heaters from Home Depot and the Bradfords Whites pull combustable thru the side of the water heater.

The AO Smith/State family and American/Whirlpool water heaters pull their combustable from the bottom.

That little 2" void under the water heater is probaly the dustiest place in the house. All the sawdust from the garage or dryer lint from the utility room or dust being move by the HVAC system ends up there.

AO Smith made a great water heater back in the day, but the missed the boat with the FVIR water heaters. They still make a decent tank but the FVIR system is flawed.

I work on alot of gas water heaters.

I work on a few Bradford Whites it's generally a bad thermocouple or limit switch. I always change both. It's a reasonable repair.

Since Rheem introduced their new FVIR around 2002 I have had to work on 2. That's right only 2 in around 11 years. The first failed because of improper venting. The second instance, I had installed a 80 and 50 gallon side by side in a unfinished basement. I got a call 3 months later that hte water was luke warm. When I arrived I found they had finished the basement and used auto-paint to make what they called art. The paint fumes caused a flammable vapor action, causing the vial to break. I isolated the 80 gal and ordered a new burner assembly.

Like I said I rarely work on the Bradford Whites and almost never work on the Rheems.

The AO Smith and American manufactured water heaters will put my children thru college.:laughing:


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## Letterrip (Jul 28, 2013)

You sir, are a gas powered genius!! (Insert jokes here). That lovely inner screen that prevents the open flame from escaping the burn chamber was nice and plugged. I see what you mean about the intake on the ground promoting problems. Based on our conversation, I lit the pilot and cracked the metal cover, and amazingly, it maintained the flame. Blew the screen out with a compressor and used the vacuum to clean out extra debris and voila!! They have hot water now. Thank you!!


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## PlungerJockey (Feb 19, 2010)

Not a genius, we have quite a few of them around here.

Glad I could help


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