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 Posted: Sun Feb 12th, 2012 08:13 am
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drew
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i have an older bradford white 40 gallon heater. that worked fine when i bought my house last march.

in may the pilot went out, so i relit it, but then it went out again after the tank had completely heated. the heater is in the laundry room. it has a bathroom fan in the ceiling and the door to the back room always stays open so it seems like there should be good enough airflow.

i had the gas company guy come out and he measured the voltage of the thermocouple, and it was right on line between good and bad, so i replaced it and nothing changed. he said if it wasn't the thermocouple then it was most likely the gas valve, which would be $100 to replace. i decided to wait.

finally today i was at lowes looking at new water heaters and spotted a gas valve just like mine, or so i thought. it had the extra wires for the thermoswitch on newer bfg whirlpool heaters, and google told me i could just jump those together and it'd work fine. so that's what i did.

well, i still have the same problem. the pilot stays lit when i light it, but goes out after the tank is done heating and the burner turns off. if i try to light it when everything is warm or hot, it usually won't light. but it lights fine when it's cold.

i'd really be fine getting a new water heater, since i don't even know how old this one is and a new would be more efficient, etc, but i don't want to spend all that money only to find out i didn't need it and the problem was low gas pressure or inadequate airflow or something.

any ideas?

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 Posted: Sun Feb 12th, 2012 01:09 pm
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Geno_3245
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Did the gas company measure the gas pressure?
Some gas control valves can be adjusted for pressure.

Thermocouple test from Rheem manual: "With the pilot flame lit, turn OFF the gas supply and start to count seconds (one-one thousand, two-one thousand). Count for a full twenty (20) seconds. The pilot flame should be out. Listen carefully for a small clicking noise at the gas inlet side of the valve. If you count for the full twenty (20) seconds and do not hear a click then the thermocouple is fine. If you hear a click within the twenty (20) seconds then the thermocouple and or gas valve is bad. Replace both the thermocouple and gas valve."

Is the burner clean, or does it have black soot that indicate insufficient air flow or slow venting or clogged burner orifice? Clean combustion parts with water and wire brush.

The pilot orifice might be dirty. Clean with carburetor cleaner. Clean pilot tube.

Make sure thermocouple is embedded in pilot flame and that pilot flame is strong and clear blue.

Is the burner flame clear blue and strong. Or is the flame yellow. Yellow indicates low gas pressure or dirty combustion parts. And or insufficient air flow. And/or bad gas control valve.

Inspect and clean flue way.

Let the burner operate until it is hot. At the vent hood on top of tank. Light a match and hold match just outside the vent hood where air is pulled in. Blow out match and see if smoke is sucked into the vent. It should draft in and upward immediately if vent is good.

Look at top of water heater for signs of sooting that indicate another gas appliance might be pushing vent gas back down water heater vent and blowing out pilot.

Close all doors and windows. Turn on all the exhaust fans and vent fans in house. Water heater burner is off. Light a match at vent hood and put match under hood and blow out match. Does smoke draft immediately upwards? Of does smoke draft downwards? Downdraft would indicate negative pressure is causing pilot to blow out.

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 Posted: Mon Feb 13th, 2012 03:13 am
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drew
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thanks for the tips. to my surprise, the pilot was still lit this morning, but went out after the next time the burner came on.

here are the results of the tests:
the gas company didn't check the pressure when they came out. my gas valve has a "main burner pressure" screw but i haven't messed with it.

i didn't try the thermocouple test, since i replaced both the thermocouple and valve already.

the burner was fairly clean. some whiteness but no heavy black soot or anything.

the pilot tube is easy to blow through, so it doesn't SEEM clogged.

the thermocouple is indeed embedded in the pilot flame.

the pilot is blue with the occasional yellow spurt. but 99% blue.

i didn't see any soot on top of the heater.

the match smoke was sucked up the vent both while the burner was operating and when it was not.


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 Posted: Mon Feb 13th, 2012 05:04 am
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Geno_3245
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It's easy for me to write a long list of stuff for you to check inside the burner while laying on the floor, and then crawling up to the roof with a limb saw. But here goes.

Gas pressure is one of the suspects.
Call gas company and ask about pressure test, and adjusting gas pressure on control, and bleeding possible air out of gas line.

Was there moisture, or dirt or flakes in the gas line when you replace control? Yellow teflon tape should be applied to gas line so that no bits of tape can break off and enter gas line and get drawn into gas control.

What is the gas flame doing? Clear blue and strong? This can indicate that gas pressure is good.
Is the flame wavy as if it is getting draft condition that might blow out pilot?
Pilot flame is clear blue and strong so it seems like pilot orifice and pilot tube are clean. Is the pilot wavy as if draft condition might blow out pilot?
A spider-web-sized obstruction can cause pilot problems.
It wouldn't hurt to clean the parts and eliminate that from suspect list.

Dirty combustion parts are suspect.
Is the burner flame blowing out the pilot? Have you observed when the pilot actually goes out? Clean the burner and burner parts according to product manual.

Bad gas control and defective thermocouple are suspects.
Try the thermocouple test, because that is also a gas control valve test.

Thermocouple should be finger tight + 1/4 turn. If thermocouple is overtightened, then it will short against gas control body, and proper milliamp is not received by gas control. Thermocouple can have gradual bends but no kinks.

Check top of roof to make sure vent roof cover is in place. A few weeks ago on this site, there was conversation about wind blowing out pilot light.
Roof vent might need to be raised, and limbs cut back from vent.

If pilot goes out when burner turns on, there may be condensation dripping back down vent that extinguishes pilot. This could be more likely if vent pipes have horizontal lengths, and also when vent pipe is exposed to cold air so that combustion by product condenses on inside of vent pipe. Install condensate tee.
Watch the burner when it turns on.

Vents inside the house are also suspects.
Did you try the vent test will all household vent fans on, and doors and windows closed?
Turn on furnace during this test and see if you can recreate draft condition that might blow out pilot.

What gas control do you have?
Take photo of old and new gas controls. There is identifying information on side of each.
Post photo of control valve on flickr or other site, then add a link to the photo or add photo directly to this site using icon.
I might have service manual for that gas control.

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