pilot light and burner won't stay lit longer than 30 seconds

[renrag]

I have two hot water heaters, one is for heating, the other for domestic hot water. On Labor day I noticed no hot water. I checked the heater, pilot was out. So I lit the pilot and turned the heater to on. Watched as the heater fired up. An hour later, still no hot water. I checked the heater and no pilot etc.. Repeated the process and watched as the burner stayed on for about 3 seconds before extinguishing. Re lit the pilot and watched, it stayed lit for 2 minutes then gradually flickered and went out. Changed the thermocouple, same result. Ran to store and replaced 6 year old heater. Replumbed new heater and fired it up. It works fine. Now it's chilly out and I go to start the water heater that heats my slab. Exact same result. The heaters are Richmond 36,000 btu's with unitrol gas valves. Both heaters are 6 years old. Could this be the gas control valve and are there bad ones out there that would only last 6 years? Is it worth replacing the valve or is another new heater on my horizon? Any help would be appreciated.

Thanks.

[Runs with bison]

The unitrols gas control valve/thermostats have been problematic (see the Whirlpool thread, about half the time the problem is the unitrol Robert Shaw valve.) Some have lasted less than a year. I would try replacing the unitrol gas control valve/thermostat first--well, second after the thermocouple. Spending $60-70 dollars beats buying a new water heater.

[renrag]

My heaters have Robert Shaw R110 RTSP valves. I see lots of those for sale but some have a different number like 66 176 368. Can I buy any R110RTSP valve? What does the other number mean??

Thanks

[Runs with bison]

I don't know on the specific one. I recommend checking with a store that sells the Richmond water heaters to see if they carry a replacement that should fit your model. You might call the manufacturer to get replacement part numbers or check against what you have available locally (if you are lucky they might even send you one for free...works with Whirlpool sometimes, in my case the store let me do a swap out and reimbursed me for my purchase when I brought the spent one in.) Sometimes there are just small changes to a generic design. Other times it is more fundamental. For some water heaters GE/Rheem use the same basic Unitrol as Whirlpool...same configuration of buttons, dials and valves/ports, but with a different dial color.

[renrag]

Just for ----- and giggles I decided to call the richmond warranty line today to see if my water heaters were still covered by any warranty. Of course they run you through some trouble shooting steps. Both of my heaters are covered but this is what is strange. I felt they both had the same problem, or at least they both acted alike. On water heater number 1 that I replaced on labor day, they advised to remove the burner assembly and with a flash light, look inside the chamber and see if the fuse is blown. Because there was no glass around it and it basically looked like a steel tube about the size of the thermo couple, they said it was a blown thermo fuse and advised me to take the heater back to where I purchased it for a replacement. Before I take it back for replacement I have to call an 800 number tomorrow for instructions. The combustion chamber was basically spotless. They advised the fuse blows when there is combustible fumes around the heater, paint, human gas, etc.. Thinking they may know what they are talking about I said nothing like that has been going on in that room but since both heaters suffered the same symptoms, maybe there is something going on I don't know about. Sooooooooo. I said, by the way I have another hot water heater right next to that one that won't light with the same symptoms. They opened another claim for me, I gave them the serial number and they said do the same thing, remove the burner assembly, look at the fuse and call us back and tell us what it looks like. So I do as they say. I removed the burner door, assembly and find a totally different picture. The entire combustion chamber is jammed with rusty deposits, like the inside of the tank has fallen onto the burner. But, after vacuuming out the chamber, I tell them the fuse looks the same, no glass and not firmly in the holder. This time the guy says " it's a blown thermo control valve, we'll send you a new one out tomorrow! I'm kind of taken back, thinking this is different solution, how do I replace that? He says they'll be a list of contractors in the mailing. So now my questions have changed a little.
First, is replacing a thermo control valve something your normal half a---ed handyman can do.
Second, why does one water heater have substantial debris in it when the other one is clean? The one with the debris is a closed system, it heats my basement floor. The transfer fluid is RV antifreeze. Why would that tank drop all that debris onto the burner?
Any help would be appreciated. Obviously I now wish I would've called the help line before I went out and bought a new hot water heater although I know they weren't available on labor day weekend.

Thanks.

[Runs with bison]

I've seen some complaints before about the thermo fuses on those types (several different brands.) I don't know what it takes to replace that since I haven't pulled one of those. The gas valve/thermostat is something a homeowner handyman can do, but you need to be careful about doing rigorous leak checks on the gas tubing, remembering to reinventory with water before starting the heat, etc. Rotating the old thermostat out isn't always easy either. Hopefully some plumbers can give you tips on that.

I can think of several possibilities for why you might have debris on one and not the other:
1. Do they share a vent stack and is the one with the deposits closest to the vent stack? If so you might be getting condensate and or scale down from the vent line and into that heater. (I used to have to remove fallen scale from a water heater burner in an old house about once every year or two and I removed the baffle and brushed the central chimney in the heater every few years.)
2. The slab heating one is sitting stagnant about half the year. Perhaps the walls are staying moist from condensation of water in the pilot flame or cooling combustion gases entering from the shared exhaust stack.
3. They might see vastly different loads and/or be set to different temperatures. At particularly low operating temperatures (e.g. cold tank start up) there is a lot of condensation on the walls of the combustion chamber and the central flue. This could result in repeated corrosion cycles.
4. Perhaps there is enough scale in the exhaust vent stack that a partial blockage is occurring somewhere? If so the draft will not be sufficient and exhaust gases will accumulate, temp will rise in the combustion chamber and the thermo fuse should shut it down.
5. Do you have to change the anti-freeze solution periodically? The additive package would be expected to eventually fail. I used to work at a facility that made ethylene glycol among other things...they used some of it for a heating loop, pure stuff, no additives, and it ate the hell out of the circulation pump impeller and suction housing. They went back to using packaged anti-freeze after that.

Sounds like a good time to inspect the vent stack thoroughly making sure it is clear from end to end.

[Gsalet]

The glass tube that broke melted or is not there can break when there is not enough combustion air, with Richmond that ussually means ether it is in a closed room or the vents on the side of the unit are covered with a water heater blanket or something, another possibility is the flue is clogged, why does the water heater used for heating have more deposits? I am guessing it is undersized for the application. when you say it is used for heating, what is it heating? how many square feet and is the heater certified for use as a boiler?
My suggestion is to have a plumber check it out. It will save you time and MONEY in the long run.
Good Luck
George