Water heater problem has me stumped..

[slag]

I have two AO Smith water heaters set up in series. I have a cold water line that feeds into a 50 gallon that feeds into a 40 gallon which then feeds the house.

I can't keep the 50 gallon water heater going. I've replaced the entire natural gas pilot assembly with this https://www.amazon.com/gp/product/B000XOEZ9U/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1 and it still doesnt work. The pilot light does not want to stay lit. After about 5 minutes of holding the pilot light button down, it will stay running as opposed to every other heater I've done this on that takes around a minute tops. I can then turn the burner on and it will stay running for awhile and then both the burner and pilot light go out. The pilot light will relight quickly though. I had the pilot light going for about 2 hours last night just to see if it would stay running but it was out this morning.

Frustrated, I bought a good USED Gas control valve, same model and everything as what I had. I drained the tank, took out the old valve, put the good used one in, and same exact results. I can swap out the entire burner assembly from the 40 gallon to see if that is what is wrong, but I'm at a bit of a loss as to why I can't keep the pilot light and burner assembly going. There's no draft, no leaking water from the tank, etc. Both heaters are fed from the same gas line with separate on/off valves. I'm stumped and not really wanting to shell out $600 or more for a water heater right now this close to Christmas.

 

[NetWareHead]

How is the gas piping to this water heater? Does the piping meet spec to feed the burner? Does your entire home gas piping meet the demand for all gas fed appliances in the entire house including meeting distance requirements? (e.g. is this heater far from the meter?) Does this water heater shutoff coincide with the firing of other gas appliances in the house?

Clog in the pipe? Disconnect the union after shutting the valve and snake the line up to the valve and to the water heater gas pilot assembly. Check the drip leg while you are at it. Its a long shot but you may have either gas starvation or clog issue...

Did your gas kits come with a new thermocouple?

Called AO Smith tech support?

You may have to call a plumber. You've done more than the normal amount of troubleshooting an involved homeowner would have done in your position. Keep us updated...

 

[slag]

Little more to report based on your questions.

I did snake out the line with a piece of wire and nothing came out and it was clear up to the T. I disconnected some of the gas piping (rigid pipe, not flexible) and made sure it was all clean and clear. I turned the valve on briefly while I had the drip leg disconnected also and it shot out a good amount of gas (both pilot lights were out already). This is original equipment from when my house was built in 2006 and has worked up until recently. The kit came with a new thermocouple.

An identical water heater sits right near it and shares the same gas line (except its 40 gallon and not 50 gallon) and works fine. It's literally right next to it.

I am checking for gas leaks as well and finding none. This is very frustrating and I hate to call in a plumber and spend a ton of money on what I've already done.

 

[gorcorps]

Have you tried it with the 40 gallon water heater gas shut off? I'd be curious if anything changes when you're only feeding the problematic one.

 

[NutBucket]

Unrelated but curious as to why you need 90 gallons of hot water? Yes, I know any heater over 50 gallons is ridiculously expensive.

 

[natto fire]

That is a tough one for sure. I'm assuming the thermocouple connects directly to the gas control valve, no circuitry in between? Certainly seems like the gas control valve is shutting off when it shouldn't.

 

[slag]

Have you tried it with the 40 gallon water heater gas shut off? I'd be curious if anything changes when you're only feeding the problematic one.

no, but that's a good idea. I'm home today so plan on trying a few things, this one first.

 

[slag]

Unrelated but curious as to why you need 90 gallons of hot water? Yes, I know any heater over 50 gallons is ridiculously expensive.

The home came plumbed this way. My house is a single story with finished basement and is very spread out. In the morning, my 3 sons, myself, and my wife all bathe and a 40 gallon doesn't cut it. I'd like to have both working because the 50 gallon is already there, so it can't be too hard to get it working. I had a high efficiency 75 gallon in my old house (big discount because it was dented) and it was very awesome. Never ran out of water, even with dishwasher, washing machine, and multiple showers going.

 

[NutBucket]

Ah. My in-laws had a big heater too (at least 75 gallon) that sprung a leak. While they do have 3 full baths they don't have a need for the large capacity so we replaced it with a 50 gallon. Ironic how a 50% capacity difference is equal to a (nearly) 50% price difference!

 

[NL5]

Why not just get a tankless? Never run out of hot water....

 

[master_shake_]

I agree with the thermocouple being bad.

I had one go on my water heater and it was the same symptoms.

 

[slag]

Why not just get a tankless? Never run out of hot water....

Wouldn't work where I have my water heater installed. The run to the outside is too long and I don't want to replumb part of my basement for it.

 

[slag]

I agree with the thermocouple being bad.

I had one go on my water heater and it was the same symptoms.

I've replaced the thermocouple. Could have gotten a bad one I guess, but even when swapping the known good one over to the 50 gallon machine, it goes out when the flame extinguishes. Same exact configuration works fine in the 40 gallon. I swapped over the entire burner assembly from the working 40 gallon to the 50 gallon and the pilot light will stay lit all day long by itself, but if I make it try to warm up the water, the flame goes out after the water heats up and take the pilot light out with it. I thought it could be an air flow problem, but the air flow is not hindered and there is plenty of clearance around the water heater and it is free of debris.

 

[gorcorps]

Given your other descriptions I don't know if this is an issue, but it's worth a look since you're running out of ideas. I'm 99% sure that my relief valve on my tank was going bad, and would spray steam/hot water intermittently down towards the burner and extinguish it. I started a shower one morning with no hot water, found the pilot light out. It relighted fine, I went to work thinking "that's weird". I went home for lunch to check on it and it was out again, and there was water on the floor (I didn't notice any water the first time though). At this point I suspected the relief valved and changed it out, and didn't have any further problems. You might want to put a bucket or something if you can under the discharge pipe of the relief valve to see if that changes anything, since it will then contain any steam/water if it's relieving. If that makes a difference, then change the relief valve.

 

[slag]

Here's my configuration. The pressure relief valve works fine, I used it when I drained the 50 gallon to allow air into the system.

The one on the right goes out, the one on the left works fine. Both are fed with 1/2 inch black pipe off a 3/4 inch black pipe (main line).

This sounds a lot like my current issue: http://www.doityourself.com/forum/w...t-light-will-not-stay-lit-when-water-hot.html

I am going to check that disk and see if it has a buildup on it that might be causing an air flow issue. I'm just about out of ideas before calling in the plumber. These things are simple enough that this shouldn't be too hard to fix. It's almost a challenge now.

 

[NetWareHead]

How is the exhaust duct drafting from problem water heater? Any excess bends or improper pitch?

What is the duct setup? Both heaters connect to a single before entering a chimney? Any blockages in either pipe or chimney? Have had it swept lately? Aluminized tape around each joint in good condition? Masonry chimney or metal pipe?

U may have either an excessive or insufficient draft to support a flame. You will need a manometer to tell you how many inches of water column the chimney pulls.

 

[slag]

Cleaning the bottom filter area didn't help. I took the exhaust apart up to where it joins the other section and its clear and clean.

Still stumped. My next test will be to leave the door area open a bit to ensure it's getting enough air and see if that's the problem.

 

[slag]

I think i got it resolved! I used my portable AC compressor to blow down through the filter instead of sucking up from below to clean out the corderite disk. I did that, cleaned every little bit as well as I could, vacuumed everything up again, blew more air, etc, and then put it back together. Pilot light was still lit this morning and the burner had just kicked on. 3 boys had showered and I just finished mine and we still had hot water. I'll monitor for a few more days but think this might have solved it.

 

[slag]

Still working this morning!!

 

[gorcorps]

Nice

Even though you already spent money on some parts, it's always nice to find out the fix was free and relatively simple.