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Old 08-07-2008, 04:47 PM   #1
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Need advice for gas hot water problem, please!!


OK, I think I know the answer, but I'm hoping someone more knowledgable than I am can offer insight into any options I might have overlooked.

I left my home in TX for 6 weeks to go to Kansas for a rather involved project. Rather than turning the water heater off, I simply changed the control setting to "pilot light". When I got back to TX, I tried to restore the water heater to fully functional by simply turning the control back to "on".

Well, the pilot light is fully operational, so the thermal couple isn't the problem, but I can't seem to get the burner to light, no matter where I set the temperature setting.

I suspect I need a new gas valve (a project I've tackled in the past, so I'm sure I can do that myself).

However, as I am not a trained plumber, I am ready to admit there are probably lots of possibilities of which I am not aware. Does anyone think I'm missing anything here, or should I head for the store to get a new valve?

Thanks for whatever help you may be able to offer!!

Dugly

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Old 08-07-2008, 05:15 PM   #2
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Need advice for gas hot water problem, please!!


This is a truly excellent question, but not for the reason you may be thinking.

You probably already know that a thermocouple gradually produces less voltage with time, and at some point the voltage produced by a thermocouple isn't enough to keep the safety valve electromagnet on the gas valve open, and gas stops flowing to the pilot light. So, in that case, replacing the thermocouple would fix the problem and allow the pilot light to stay on so the gas valve can operate properly.

BUT, water heaters don't use thermocouples. Only boilers and furnaces use thermocouples because boilers and furnaces have an outside source of 24 VAC power to operate the main electromagnet in their gas valves. Thus, on a boiler or furnace, the thermocouple in the pilot light generates a few millivolts which is used to hold an electromagnetic "safetly" valve inside the gas valve open that allows gas to flow to the pilot light. The main electromagnetic valve, the one that allows gas to flow to the burner trays, operates on 24 VAC power from outside, and is switched on and off by the thermostat. (no to put too fine a point on it, it's typically switched on and off by a relay which is controlled by the thermostat)

Older water heaters (the ones without flue dampers) don't have outside power supplied to them. So in an older water heater, the pilot light flame has to generate all of the power needed to operate BOTH electromagnetic valves inside the gas valve.

To generate more electrical power from the pilot light flame, a water heater will use a thermoPILE, not a thermoCOUPLE.

A thermopile is nothing more than a whole bunch of thermocouples all connected in series so that instead of producing a few millivolts like a thermocouple, a thermopile produces a whole volt or so. The additional power is needed to operate the main valve to the burner trays.

But if a thermocouple produces less voltage with time, then it stands to reason that the same thing would happen in a thermopile. And it also stands to reason that if the thermopile was producing enough voltage to keep the safety electromagnet open, but not enough to keep BOTH the safety and main electromagnets open, then replacing the thermopile would solve the problem.

Follow?

I'd like to hear from someone knowledgeable about this as to whether the voltage produced by a thermopile declines with time just like that of a thermocouple. And, whether the result of this could be that the safety electromagnet on a water heater's gas valve would have enough power to stay open (so the pilot light remains on) but there wouldn't be enough power to open the main electromagnet, so that the burner trays never come on.

In that case, replacing the thermopile WOULD fix the problem.

If you have a thermocouple, you will have what looks like a thick copper wire going from the thermocouple in your pilot light to your gas valve. If you have a thermopile, you will will have two small wires with crimped connectors on their ends coming from the thermopile in the pilot light to screw connections on your gas valve.

Also, before replacing the gas valve I think it would be a good idea to take the cover off the thermostat and simply jumper the terminals on the thermostat. It is possible that the thermostat simply isn't closing the circuit to the gas valve main electromagnet. Jumpering across the thermostat would eliminate it as a possible cause.


Last edited by Nestor_Kelebay; 08-07-2008 at 06:05 PM.
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Old 08-07-2008, 07:52 PM   #3
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Need advice for gas hot water problem, please!!


Quote:
Originally Posted by Nestor_Kelebay View Post
If you have a thermocouple, you will have what looks like a thick copper wire going from the thermocouple in your pilot light to your gas valve. If you have a thermopile, you will will have two small wires with crimped connectors on their ends coming from the thermopile in the pilot light to screw connections on your gas valve.

Also, before replacing the gas valve I think it would be a good idea to take the cover off the thermostat and simply jumper the terminals on the thermostat. It is possible that the thermostat simply isn't closing the circuit to the gas valve main electromagnet. Jumpering across the thermostat would eliminate it as a possible cause.
It must be a thermocouple--there are 4 connections to the gas valve. The gas supply line enters the valve about the middle of the left side of the valve. There are 3 more "pipes" that enter the valve, all 3 from the bottom. There is that copper one that you described, there is a silver colored pipe about 1/8" diameter that supplies the gas to the pilot light, and there is another silver colored pipe that is about 3/8" in diameter that courses from the gas valve to the bottom of the area where the burner is (although I cannot see a connection to the burner, that pipe seems to run underneath a bracket that is about 3" high and supports the burner). The label on the side of the gas valve reads "9535 Robert Shaw Unitrol".

Noob question here, how do I remove the thermostat cover? It appears to be secured to the valve assembly by 4 screws, one at each corner, but the rotary dial that is used to set the desired temperature doesn't seem to be willing to come off. Is it possible that the dial comes off with the cover?

FYI, I can clearly hear a very audible "click" as I rotate the thermostat knob past halfway. Here in TX, the garage gets hot enough that the water in the tank is adequately warm, simply from just being located in a non-airconditioned area of the house, for me to take a rather lengthy comfortable shower if I use only the hot water !

The water heater is about 14 years old. It is a Sutherlands product. Since it appears to have a thermocouple, I may go to Sutherlands and attempt to find a replacement--that's relatively cheap for a starting point.

Thanks, Nestor--b/c of your excellent explanation regarding the function/purpose of the thermocouple, I now understand why the pilot light could remain lit and yet the thermocouple could still be defective. If I can get the thermostat cover off, I'll try jumping between the contact points to r/o the thermostat as the problem.

Dugly
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Old 08-07-2008, 10:12 PM   #4
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Dugly:

Normally the thermostat on a water heater is located about 2/3 to 3/4 of the way up the tank and is located on the exterior metal jacket of the heater, outside the insulation. There is a threaded hole in the exterior wall of the tank that the thermostat screws into so that the temperature probe is inside the hot water.

If you're thermostat is located way down near the burner trays, then it's a completely different set up than I'm used to seeing, and I'm as clueless as to how to remove the cover on that thing as you are. If you hear an audible click from the thermostat as you turn the dial past the water temperature inside the tank, that's a good indication that the thermostat is working, but it's not conclusive.

If you say you have what looks like a fairly large diameter bare copper wire (kinda like a copper capillary tube) going to the gas valve, then that is a thermocouple, NOT a thermopile. If you have a thermocouple, that would be the first time I've heard of a thermocouple on a water heater. Normally, a stand alone water heater will use a thermoPILE. If you have a thermocouple, then I agree that your original diagnoses that the gas valve needs to be replaced is probably correct. If you actually have a thermopile, then that is where I pose the question: "Could the thermopile be producing enough power to operate the safety electromagnet, but not both the safety and main electromagnets."

It is ONLY if you have a thermoPILE that the possibility exists that the problem is an old thermopile. If you have a thermocouple, and the pilot light stays on, then the problem is most likely a bad gas valve.

Look at where that "copper pipe" connects to the gas valve. If it's just a knurled nut, then you have a thermocouple.

I would contact some of the plumbing companies in your area and ask them who would be knowledgeable about old Robertshaw Unitrol gas valves in your area, perhaps a company that sells heating controls. Find out as certainly as you can whether your hot water heater uses a thermocouple or a thermopile. Even take some digital pictures of the gas valve so they can see where that copper wire connects to the gas valve.

(PS: that copper "wire" is actually a co-axial cable, or one wire inside another with insulation between them. At the thermocouple in the pilot light flame, the interior and exterior wires come into contact, and a voltage is generated in the interior wire as long as the junction between the wires is hot. The coax cable carries that tiny voltage to the gas valve to hold the safety electromagnetic gas valve open for the gas to flow to the pilot light.)
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Old 08-07-2008, 11:07 PM   #5
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Quote:
Originally Posted by Nestor_Kelebay View Post
Dugly:
Look at where that "copper pipe" connects to the gas valve. If it's just a knurled nut, then you have a thermocouple.
All 3 of the tubes at the bottom of the gas valve attach with hex nuts, through which the "tubes" enter the valve body--looks like a job for a flare-nut wrench. There are no electrical connections, only that one "copper pipe" you've described so accurately.

I'll see if I can post a photo--never seen one on this forum, but I'll give it a try--computer malfunction necessitates that I add the photo after I've posted this message, so check later to see if I have figured it out.

You can clearly see the copper "capillary tube" (for lack of a better term) in this photo.




Here's a photo of the front of the water heater, you can see the method of construction--there's nothing else on the back or the sides:



And finally, a shot from below the gas valve:



This is the first time I've seen the bottom of the gas valve, LOOK at those two red wires at about 1:30 from where the capillary tube enters the valve--do you suppose that's the two wires of which you spoke? I don't see any crimped connectors or screw connections, but there they are, bright as the light of day, 2 wires--any ideas?????

Thanks for all the advice, Nestor!

Dugly

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Old 08-08-2008, 07:32 AM   #6
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Need advice for gas hot water problem, please!!


You have a thermocouple. If the pilot stays lit in the on position, you will need a gas valve. How old is your tank? Compare the cost of replacing the valve and the entire tank.
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Old 08-08-2008, 08:24 AM   #7
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How old is your tank? Compare the cost of replacing the valve and the entire tank.
The tank is 14 years old at least--yeah, I figure there might be a point of diminishing returns regarding the amount of $$ that might be involved , It's not that difficult of a job to replace the whole unit; I installed this one myself, can most assuredly take it out and replace it if need be.

Thanks!

Dugly
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Old 08-08-2008, 08:59 AM   #8
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Quote:
Originally Posted by Nestor_Kelebay View Post
Dugly:
Normally the thermostat on a water heater is located about 2/3 to 3/4 of the way up the tank and is located on the exterior metal jacket of the heater, outside the insulation. There is a threaded hole in the exterior wall of the tank that the thermostat screws into so that the temperature probe is inside the hot water.
OK, onward through the fog! I've taken this photo from the side of the valve--it's not the best of photos, but if you look carefully you can see a brass flange protruding from the tank to which the gas valve is attached. At first I thought "Great! I've found where the thermostat is mounted on the tank", but it's not quite aligned with the center of the heat adjustment knob, in fact the center of the "thermostat" knob would be at the same level as the bottom of the flange.



So, am I correct, is this where the thermostat enters the tank? If so, do I have to drain the tank in order to remove the gas valve, or is the thermostat encased in some sort of sleeve that would allow me to remove it without going to all the trouble of draining the tank?

As you can see, I'm considering replacing the valve assembly--still waiting for Sutherlands to open (since it's one of their water heaters, I figure they might have gas valves in stock), so right now it's once again just scheming/dreaming time!!

Dugly
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Old 08-08-2008, 10:10 AM   #9
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Dugly: I agree with 47-47.

That thick copper wire is definitely at thermoCOUPLE. This is the first time I've seen a gas valve operate entirely on the tiny voltage produced from a single thermocouple.

This is also the first time I've seen a combined gas valve and tank thermostat.

I agree with your original assessment that the problem is your gas valve. You need to replace the gas valve. But, the valve is gonna cost $100 or so, and you're gonna have to pay that much again in labour for someone to do it for you. You're looking at $200 for the repair. A new tank installed is gonna cost about $400.

I think it's more economical to replace the whole tank at this point.
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Old 08-08-2008, 10:59 AM   #10
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Quote:
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Dugly: I agree with 47-47.

I agree with your original assessment that the problem is your gas valve. You need to replace the gas valve. But, the valve is gonna cost $100 or so, and you're gonna have to pay that much again in labour for someone to do it for you. You're looking at $200 for the repair. A new tank installed is gonna cost about $400.
Well, it's good to know that great minds think alike!

I'm pretty handy, have all the tools needed to do this valve repacement, so I may attempt it myself if it's a simple R & R process. My only concern right now is whether or not I need to drain the tank to do the job--as you can see from the photos, I replaced the factory spigot with a good quality brass faucet before I even installed the heater, and the tank is elevated about 18" above floor level, so I can drain it if need be.

Not having any experience with valve replacement, I can only ask--is this a simple R & R, or are there factors of which I am unaware that might make it a bad idea to attempt the repair myself? I'm familiar with how to make sure the gas supply line isn't leaking, etc., just wondering if once I take those "tubes" off and pull the valve there will be any surprises........

Any ideas if that thermostat is in a waterproof sleeve or not? I just replaced a 40-gallon gas fired hot water heater with an electric whole house HWOD unit in a vacation/project/retirement home in KS, and started to disassemble the heater so I could use the intact tank for a solar heating project--wish I had gotten all the way to the thermostat , then I might know the answer to my own question!

I guess the first step is to take the info from the side of the valve and head for Sutherlands--in the meantime, if anyone knows if the tank needs to be drained or not, please inform me.......

Before I head for Sutherlands, though, it's time for one more hot water shower, courtesy of the heat soaked up from the hot garage--hey, I could just put this off till the weather gets too cold to provide passive heat---naah!

Like I said before, onward through the fog...........................

Thanks, again. to all y'all who have responded!

Dugly

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Old 08-08-2008, 03:44 PM   #11
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Need advice for gas hot water problem, please!!


Ten years is considered the life of a water heater. I say just replace it.
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Old 08-08-2008, 04:02 PM   #12
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I agree that the wisest decision would probably be to replace it.

Dugly:

If you want to try your hand at replacing the gas valve, the first step is to find out if and how to separate the gas valve from the thermostat. From what I can see, it's a combination gas valve and thermostat, in which case it may cost a lot more than $100. Also, you need to find out if that whole assembly screws into the side of the tank, or mounts on the side of the tank some other way.

Even if removing the gas valve requires unscrewing that whole assembly from the tank, you can still do that without draining the tank. You just shut the cold water inlet and hot water outlet isolation valves to the heater. Then, get your new thermostat/gas valve ready with teflon tape (or pipe dope) on the threads. Unscrew the old assembly and immediately screw in the new assembly.

Very little water is going to come out of the tank when you remove the old assembly because that would create a partial vaccuum inside the tank. You might get a hard spray of water when you first remove the assemby, because of the pressure in the tank. But, as soon as the pressure in the tank is released, any further flow of water out that hole is going to result in a partial vaccuum inside that tank, which will very much slow the rate of water flow out of that hole.

That is, as long as you keep the cold inlet and hot outlet valves closed while replacing the thermostat/gas valve, it shouldn't be a problem to do that without draining the tank.

But, I reitterate, This is an old hot water heater and you're wanting to spend from $100 to $200 fixing it yourself. You may end up with a $200 gas valve you can't use, and spending another $400 to pay a plumber to replace the whole tank.
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Old 08-08-2008, 04:21 PM   #13
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Well, by now I've been to the plumbing supply store and found out they carry a valve that is almost a direct replacement--I say "almost" b/c the service rep said that model is available with thermometers of two various lengths. I was able to see how the entire valve assembly mounts to the tank, via a 3/4" brass male thread, so it's obvious that the tank needs to be drained to replace that. It's draining right now, once that's done I'll pull the valve assembly and see which length thermometer it has so I can get the right one if I decide to fix it.

I've gone to great lengths to maintain this hot water heater, flushing it with a garden hose every 6 months or so, even using it as a supply source for a high pressure washer I use every now and then. There are no "popping" noises when the unit heats up, leading me to believe the maintenance efforts have helped eliminate scale buildup at the bottom of the tank. As a matter of fact, when I started draining it today, the water ran clear from the start, with absolutely no solid contaminants being flushed out.

Maybe that's why it's lasted this long if the life span of a hot water heater is 10 years--it's a gamble right now--replace a $100 valve and have the tank fail soon, or replace the $300 water heater when the $100 valve might provide more productive years??? Oh, my, oh, my, what to do????

I'll pull the valve assembly from the tank at least. That way maybe I can visualize the inside of the tank with a flashlight, that might give me some idea of what's built up in there. At that point, though, there has to be a go/no go decision regarding replacing the valve--I'll let you know what it turns out to be!

Sure wish I could afford a gas-fired HWOD unit! I really like the electric one I have in my Kansas home and really like the idea of not enriching the gas company for keeping a 40 gallon tank of water hot 24 hours a day--I'm a retired empty nester, so you can imagine how little hot water I actually use in a day--most days it is just a shower in the morning and washing hands throughout the day. HWOD units make sense for me (although, if you want an entertaining read, you'll enjoy my adventures involved in replacing my gas tank-type water heater with an electrical HWOD unit in the KS vacation/project home--I figure I have $2500 in the conversion effort--talk about a fiasco !!!!).

Once again, guys, thanks so much for sharing your expertise in this matter! I'd have never had the confidence to attempt this repair had it not been for all y'all!

Dugly
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Old 08-08-2008, 05:49 PM   #14
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Need advice for gas hot water problem, please!!


if the thermoC is holding the pilot light then it is at the main gas the valve is shot,and the manufacturers are not going the add a well so the gas valve can be changed .10 years as mentioned is the designed life(you must have good water in you area)new valve vs new heater might come across a dumped HWH with a busted tank might clip the valve it is a standard male connection into the tank.
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Old 08-10-2008, 07:33 PM   #15
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(you must have good water in you area)
Perhaps, the thermometer probe is very clean. I doubt that the tip is suppose to look like this, though:



Here's a shot of the area where the thermometer probe inserts into the valve--not much there):



And you can see from this photo that there's no scale buildup on top of the probe:



I'll attach a plastic spoon to a coat hanger tomorrow, try to scrape the bottom of the tank--at this point, I can't see any appreciable scale buildup with a flashlight. Might have gotten lucky--I have flushed the tank every 6 months or so, but I'm sure our city's water supply must have something to do with it.

Not bad for having been in service 14 years, eh ?

Dugly


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