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Old 10-12-2008, 10:36 AM   #1
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Is the gas valve bad?


I have a small boiler that the pilot light will not stay lite. I have replaced the thermocuople and the the mila volts DC current on the thermocuople while it's under a load. I have 30 mila volts of current. I have held the lite pilot button in for several minutes and when I let it go, the pilot light goes out. Do we have a bad gas valve or what else may be causing this.

Thanks ahead of time for any help.

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Old 10-12-2008, 11:29 AM   #2
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Is the gas valve bad?


If the pilot is enveloping the top quarter of the t'couple than I would say the valve is bad. But make sure that the flam is a nice soft blue flame and not hard and blowing.

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Old 10-12-2008, 11:46 AM   #3
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Is the gas valve bad?


Thanks for the reply HVAC lover. The flame is like you described. I also forgot to mention that this is a propane gas, but the pilot flame is good and strong and is engulfing the thermocuole fine. Think I need a new gas valve.
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Old 10-12-2008, 11:51 AM   #4
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Is the gas valve bad?


The gas valve may or may not have an ECO.
If it has 2 wires at the thermocouple fitting, it has an ECO.

Meaning it could be the gas valve, or a safety doing its job do to a control failure, or wiring short.
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Old 10-12-2008, 11:59 AM   #5
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Is the gas valve bad?


Interesting thought beenthere. It does not have two wiries at the thermocouple fitting though . An ECO? does this stand for elecronic cut-out.
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Old 10-12-2008, 12:05 PM   #6
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Is the gas valve bad?


ENERGY CUT OUT

A left overfrom GE furnac production.
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Old 10-12-2008, 12:08 PM   #7
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Is the gas valve bad?


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Originally Posted by beenthere View Post
The gas valve may or may not have an ECO.
If it has 2 wires at the thermocouple fitting, it has an ECO.

Meaning it could be the gas valve, or a safety doing its job do to a control failure, or wiring short.

He's measuring 30mv at the vavle. If the ECO was tripped there would be no reading and the pilot would be out. (OK Been, tell me where i missed the boat lol).
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Old 10-12-2008, 12:20 PM   #8
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Is the gas valve bad?


He never said how he was reading the voltage at the valve under load.(what is he connecting his meter to?)

He also said the pilot goes out when he leaves the pilot button go. Which is what an ECO would do in a safety mode.
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Old 10-12-2008, 12:30 PM   #9
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Is the gas valve bad?


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He never said how he was reading the voltage at the valve under load.(what is he connecting his meter to?)

He also said the pilot goes out when he leaves the pilot button go. Which is what an ECO would do in a safety mode.
And so would a weak pilot operator.

The ECO breaks the t'couple circuit so would it not read zero with the pilotknob pressed in?
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Old 10-12-2008, 12:43 PM   #10
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Is the gas valve bad?


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And so would a weak pilot operator.

The ECO breaks the t'couple circuit so would it not read zero with the pilotknob pressed in?
No, you would still be able to read voltage across the terminals.

When I do test a thermocouple, I use a J block, and read across its terminals to see what I read under load.

I just unscrew the thermocouple, screw the block in, and the thermo into the block. Hook my meters alligator clips to the block terminals, light the pilot, and read my voltage, or lack of.

Using clips, I can hold the button down with one hand, light the pilot with the other, and read the thermo at the same time.

After the pilots lit, I can scratch my head with my free hand, while still watching the readings.

I seldom test thermos anymore.
I install a new one.
If the valve is bad instead. No problem. I don't install new valves and leave old thermos in.

No customer wants to pay for a new vavle, and a week or so later. Pay another fee to have someone come out and install a new thermo.
Let alone, I don't want to get out of bed at midnight for free because I left an old thermo in.
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Old 10-12-2008, 12:54 PM   #11
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Is the gas valve bad?


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No, you would still be able to read voltage across the terminals.

When I do test a thermocouple, I use a J block, and read across its terminals to see what I read under load.

I just unscrew the thermocouple, screw the block in, and the thermo into the block. Hook my meters alligator clips to the block terminals, light the pilot, and read my voltage, or lack of.

Using clips, I can hold the button down with one hand, light the pilot with the other, and read the thermo at the same time.

After the pilots lit, I can scratch my head with my free hand, while still watching the readings.

I seldom test thermos anymore.
I install a new one.
If the valve is bad instead. No problem. I don't install new valves and leave old thermos in.

No customer wants to pay for a new vavle, and a week or so later. Pay another fee to have someone come out and install a new thermo.
Let alone, I don't want to get out of bed at midnight for free because I left an old thermo in.


LLOOOOOONNNGGG time ago was interviewing for a position and the SM asked how to check a t'couple. What I told him he didn't like (I described measuring the mv) he said no. He told me you blow out the pilot and if it's good the operator would close in three minutes and the t'couple was good too. I remember reading that in Honeywell. But you and bot h know that test leaves a lot of room for error.
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Old 10-12-2008, 01:03 PM   #12
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Is the gas valve bad?


LOL, yea, that was the old old way.

HW then came out with disposable t couple testers.
Never used them. But I thought it was, a bit of a bogus thing to sell.
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Old 10-12-2008, 01:41 PM   #13
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Is the gas valve bad?


The initial call was a pilot light that would only stay lite for 10 minutes or so on a residential boiler. Upon arrival I found that the thermocouple had been replaced by the home owner. The problem was the thermocouple's reataining clip had slid up on the thermocoples probe and the flame was not engulfing the thermocouple correctly. I fixed this problem and whlie I had the pilot assembly out of the unit I thought even though the thermocouple was new and the pilot flame appeared good and strong I should check the current and clean the pilot assembly , orfice, and tube. With the end of the thermocouple out of the gas valve I hooked the aligator clip here and the other aligator clip from my meter leads to the thermocuoples wire for a ground. This measured 30 mili volts DC current while holding the pilots button in to keep the pilot lite. So i reassembled the pilot assembly back into the unit, switched the gas valves knob to "on" , burrners come on and everything looks fine. I stayed and cycled the burrners threeor four times and watch the temp. heat the water to 180 degress. This was three days ago. I get a call from the home owner today and he says that is cannot keep the pilot lite. he holds the pilot button in for several minutes and the pilot always goes out.
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Old 10-12-2008, 01:53 PM   #14
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Is the gas valve bad?


Quote:
Originally Posted by Gargecko View Post
The initial call was a pilot light that would only stay lite for 10 minutes or so on a residential boiler. Upon arrival I found that the thermocouple had been replaced by the home owner. The problem was the thermocouple's reataining clip had slid up on the thermocoples probe and the flame was not engulfing the thermocouple correctly. I fixed this problem and whlie I had the pilot assembly out of the unit I thought even though the thermocouple was new and the pilot flame appeared good and strong I should check the current and clean the pilot assembly , orfice, and tube. With the end of the thermocouple out of the gas valve I hooked the aligator clip here and the other aligator clip from my meter leads to the thermocuoples wire for a ground. This measured 30 mili volts DC current while holding the pilots button in to keep the pilot lite. So i reassembled the pilot assembly back into the unit, switched the gas valves knob to "on" , burrners come on and everything looks fine. I stayed and cycled the burrners threeor four times and watch the temp. heat the water to 180 degress. This was three days ago. I get a call from the home owner today and he says that is cannot keep the pilot lite. he holds the pilot button in for several minutes and the pilot always goes out.
The valve or something keeps blowing out pilot.

Burner concussion maybe?



BeenThere your turn LOL
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Old 10-12-2008, 02:52 PM   #15
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Is the gas valve bad?


That is not testing it under load.

Under load, would be while its hooked to the gas valve.
I found a lot of t couples that will test good that way, but are weak. When tested underload, they test out at 20 or less mV.

The clip could be bad, and letting the t couple slide away from the pilot flame.

If its not.
Install a block, and check it while under load. If it test ok then. You probably have a bad gas valve.

Keep in mind, that if it is a gas valve. You should still install a new t couple.

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