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Old 12-30-2010, 02:52 PM   #1
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1971 18' Caravel
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Water Heater Pilot won't light

I just replaced the water tank for my original (1970) Safari. Before ordering the replacement tank I tested the pilot and gas valve operation and everything worked properly. Once all the parts were put on the new tank, the water heater installed and hooked up, gas shut off valve turned to the on position, positive test for gas at the water heater, but now I can't get the pilot to light. Any ideas? I see that the gas valve that the thermo couple and pilot connect to has a face plate with three screws. Is it worth trying to open and clean? Any help is appreciated.
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Old 12-30-2010, 03:24 PM   #2
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Pilot

Is it that the pilot won't lite or it won't stay lit?
Did you remove the thermo couple from the gas valve when you replaced the tank?
Try removing the thermo couple line from the gas valve and clean the end that goes into the valve as well as the point in the valve where it makes contact. There is a very small current involved here and the slightest bit of oxidation could cause a problem.
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Old 12-31-2010, 01:43 PM   #3
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The pilot won't light at all. I did remove the thermo couple from the gas valve, but only after it wouldn't light. I didn't clean the connection, but did ck ok for air flow. BTW, how is the current generated? Do you know anything about the inner workings of the gas/pilot valve mounted on the tank?
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Old 12-31-2010, 02:49 PM   #4
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In your first post you stated that the valve was in the on position. Typically when you lite the pilot, the knob should be in the pilot position and you have to press it in while lighting the pilot. I am assuming you know this since you said you had it lit on the old tank.
How did you determine that you have gas at the valve?
The pilot orific is very very small; If you've had the system apart, it will take a long long time to bleed the air out of the line thru the pilot orific.
When you said you check for airflow. What air flow?
The thermo couple unit is a sealed unit. When the tip of it is heated there is a very small amount of current (Milliamps) generated. The opposite end of the thermocouple line slips into a hole in the valve and a nut is tighted to hold it in place. Down inside that hole there is a coil of wire that operates the valve, and the end of the thermocouple must make mechanical contact with its mating part inside the hole.
By pressing in on the knob to lite the pilot, you are only allowing gas thru the pilot orific and overriding the safety in order to get the pilot lit.
Once the pilot is lit and will stay lit when you let up the knob, the small amount of current thru the thermocouple will hold the valve in the "safe to operate mode"
Then when you turn the knob on the valve to the "ON" position and if the thermostat calls for heat, the burner will light.

You need to get the pilot to lite before you can tell if the thermocouple is working and will hold the valve in the "safe to operate position" once you let up on the knob.

My guess is that you either don't have gas to the valve or the pilot orific is plugged and won't let the gas thru.

At your own risk!! You could open the valve on the propane tank slightly, then loosen the gas line fitting at the water heater gas valve and bleed the air out of the line. Of course the shut off valve below the belly pan would also have to be opened. Let it bleed for 3 or 4 minutes, then tighten the fitting on the valve. Get your soap bottle out and check for leaks before you try to lite the pilot again.

Can you post pictures of what the set up is?
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Old 12-31-2010, 03:15 PM   #5
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Here is another explanation of how the thermocouple works.

How Thermocouples Work in Gas Water Heaters

All gas water heaters use pilot lights to ignite the main gas burner used to heat the tank reservoir. The pilot light plays a significant safety role as it ensures that any gas supplied to the main burner is immediately ignited and not allowed to accumulate prior to combustion, thus creating a potentially dangerous explosion.
The thermocouple in a gas water heater stands guard over the functioning of the pilot light. It accomplishes this by continually monitoring whether the pilot light is burning and by providing an immediate "fail safe" by shutting down gas supply system when the pilot lights fails to burn, before uncombusted gas can accumulate at the burner head.

The thermocouple is deployed so that the tip (junction of two dissimilar metals) of the thermocouple is positioned directly into the flame of the pilot light. In the thermocouples used in most water heaters, the heat from the pilot light will generate a current measuring 20 millivolts in the thermocouple circuit. This voltage is sufficient to control and hold in the "open" position the gas control supply valve to the pilot. The current will flow and the supply valve will remain open, allowing gas to flow as long as the flame is lit, but once the flame fails, the temperature drop, reduces the current required to open the valve and the gas supply is closed off, preventing excess gas buildup.
In many systems, both the pilot and main gas supply are controlled by temperature-generated voltage. In these installations the thermocouple is replaced with a thermopile which sends current to a system thermostat, controlling gas feeding to main burner which closes down any gas supply once the pilot is extinguished.
The effective use of the thermocouple and the thermopile is responsible for a "fail safe" system which has dramatically improved the safety performance of gas fired appliances and furnaces, making these among the most safe in the heating industry.

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Old 01-01-2011, 08:44 PM   #6
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Very good information, THANKS. I can post pics if necessary. I understand your discription of the various componants and what each does. I've been lighting pilots for years and am aware of how long it takes to bleed the air out of a line. So, I will try to describe once more, using the proper names of the componants. There is gas in the tank, stove, oven and furnace, and they all operate as they should. The shut off valve on the supply line to the water heater is turned on and there is gas present at the control valve. The pilot line that comes out of the bottom of the control valve has been removed and checked for obstructions to which there are none. So in theory, that should mean that if I have the knob on the control valve turned to pilot (which it is) and depress the button to send gas through and to the end of the pilot line, I should be able to light the pilot. My problem seems to be that I'm not getting any gas out of the control valve for the pilot to light and then warm the thermo-couple sufficiently enough for the pilot to remain lit. So, I come back to my original question; The gas control valve has a face plate with three screws securing it to the body of the control valve, which should mean that is servicable. Can/should the control valve be opened by removing the cover to discover why it isn't permitting gas to flow through to the pilot? If the answer is no, would I then need to purchase a new control valve? It's puzzeling because everything worked properly before changing the water tank, and if you've been through that process you know that gas control valve threads into the tank as one unit, without any disassembly of the control valve. So, if the control valve is defective it's just a coincedence and not due to removal and reinstall. I have done this a few times in the past on other A.S. projects without a problem. Still hoping you can help. Jeff
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Old 01-01-2011, 09:58 PM   #7
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Look for a pilot adjustment screw. Is there any pilot flame at all? Maybe when you were removing and reinstalling it, a chunk of dirt or rust broke lose and is plugging up the orific. If the 3 screw cover looks like it will come off. I'd try it; at least you'll find out what's behind it.
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Old 01-05-2011, 04:49 PM   #8
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Pilot

Jeff; Did you get it to work?
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Old 01-06-2011, 04:53 PM   #9
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Haven't had a chance to work on it yet, it's either the weather or my schedule keeping me from it.
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Old 03-10-2011, 07:56 AM   #10
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Finally had a chance to work on the gas valve. I removed the valve so I could work on it more easily on the work bench. Removed the face-plate for inspection and could find no problems. What I did discover was that the pilot adjusting screw was preventing any flow what so ever. I slightly opened the screw and could then get flow. I reinstalled the gas valve and the pilot lighted right up, no problems. I have also readjusted pilot for blue flame too. I should have checked the pilot adjustment earlier, but didn't have reason to since I didn't make any changes to it. Thanks for your help.
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