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Anonymous Posted on Mar 25, 2011

I have a Marco gas fireplace model# 794019C. It is the millivolt pilot generator type. I first changed the thermopile and cleaned the spark ignitor to get it to light. I have checked continuity and everything checks out. Damper switch opens and closes, burner wall switch is good. When I jump the the redundant gas valve with jumper wire from one of the three terminals it does turn the burner on. Some of the time it is hard to keep pilot light lit, it will trip gas valve when you move from pilot to on position. The only thing that I think it could be is the gas valve! Please give me some advice. Thank you. Mike

  • Anonymous Apr 08, 2011

    Advice was given to me in regard to a possible bad thermocouple! I do not have a thermo couple I just have a thermopile as I explained. I replaced the thermopile before. The advice that I recieved did not make sense. Please try to help me understand. Thank you so much.

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  • Master 4,736 Answers
  • Posted on Mar 25, 2011
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Mike, I suspect that the problem you're having is not related to the new Thermoplie (Pilot Generator) you installed. Its with the Thermocouple. The clue was "Some of the time its hard to keep the pilot light lit". The Thermopile controls the opening and closing of the gas valve, when the wall switch is turned ON/OFF. The Thermocouple, is what keeps the gas valve open and pilot light lit all the time. If there's no flame heat on the Thermocouple, it closes the gas valve. Rather than replace it, you can try polishing it with some very fine sand paper, then wipe the tip with a cotton ball soaked in alcohol. If the Thermocouple is really pitted, don't attempt this. Just replace it. If you do replace it, when you make the connection to the gas control valve, finger tighten the nut, then tighten only 1/4 turn more with the appropriately sized wrench.

By the way, MARCO is no longer in business as MARCO Fireplace. It was purchased by Lennox Hearth, a division of Lennox Heating. And your model firsplace is no longer manufactured. If you continue to have problems with it contact Angie Parrish at Lennox via email [email protected].

Hope this helped you solve the problem. Please be kind enough to rate my response to you. Thanks and have a good day!

  • Anonymous Apr 08, 2011

    If you only have a Thermopile are you certain that you connected the 2 wires to the TH and TPH Terminals on the control valve milivolt block. If not , it won't work. Now, lets get down to the nitty gritty. Where did you purchase the Thermopile and how did you determine that you purchased the right one? Not all Thermopiies generate the same amount of voltage. If the one you purchased was below the minimum required, that would be the problem.

    If, as you think it's the gas control valve, I can tell you this, they are not inexpensive to replace. With a fireplace as old as yours and is no longer being manufactured, you may want to consider replacing the entire firebox with one that's new and more efficient.

    Also, I would be curious as to what Angie Parrish advised you to do? Please advise. Thanks

  • Anonymous Apr 08, 2011

    If you only have a Thermopile are you certain that you connected the 2 wires to the TH and TPH Terminals on the control valve milivolt block. If not , it won't work. Now, lets get down to the nitty gritty. Where did you purchase the Thermopile and how did you determine that you purchased the right one? Not all Thermopiies generate the same amount of voltage. If the one you purchased was below the minimum required, that would be the problem.

    If, as you think it's the gas control valve, I can tell you this, they are not inexpensive to replace. With a fireplace as old as yours and is no longer being manufactured, you may want to consider replacing the entire firebox with one that's new and more efficient.

    Also, I would be curious as to what Angie Parrish advised you to do? Please advise. Thanks

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0helpful
2answers

Just replaced thermopile generator and pilot will not stay lit

Check the new thermopile with a millivolt meter and make sure it has the correct output not connected to the gas valve.If it does,then the gas valve is defective.Make sure to test ONLY the thermopile.If it does not generate enough millivolts the gas valve will not open.If the piliot is dirty it will not generate enough heat for the thermopile.Make sure you have a good,strong,blue flame at the pilot.You said the piliot will not stay lit?If not then start by blowing air back through the piliot where the flame comes out with compressed air.hopefully that will clean it well enough.If not you may have to take the pilot tubing loose from the valve and use compressed air to clean it.Make sure when you reconnect the tubing to the valve USE FINGERS ONLY to start tyubing or you may crossthread the tubing....and thats NOT a good thing.Good Luck.
2helpful
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How to check a thermopile generator

Log in to the Honeywell internet site and ask the question using yur model generator! It is probably supposed to produce a spark that may be regulated.
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Kozy heat 932 fireplace, pilot goes out when i release the knob, I get 17.5 millivolts on the thermo coupler

the thermopile needs 600 millivolts from that for it to work, clean pilot recheak thermocouple if still low change it .
0helpful
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What is the problem when millivolt gas valve can not keep it pilot on?

Hi there.
Probably the thermopile is not receiving enough heat from the pilot flame to generate 500 to 750 millivolt to hold pilot flame. The thermopile may have soot or dirt on it so try to clean or the pilot flame itself does not give enough heat, try adjusting pilot flame. Or the thermopile could not generate the right amount of millivolt even if it is clean and receiving enough heat from pilot flame, so better replace the thermopile.
Check also the hi limit, it must have continuity across its terminal.
Regards
1helpful
1answer

I replaced the gasvalve and thermalpile in my 35,BTU wall heater I light the pilot and turn the heat on it goes out I ran a new state wire in case of a short but it still does it, did I get a bad...

Did you get the right gas valve for a thermapile and not a 24 volt gas valve? Also I would recheck my wiring.... Here is a article that may be of HELP....... Hope this Helps.....
Thermocouple: A thermocouple is a device made of two different metals which creates a small electrical charge when heated at one end.
Thermopile: A thermopile is a probe that contains multiple thermocouples, therefore it can produce a larger electrical current. Millivolts: 1/1000 of a volt - thermocouples and thermopiles typically produce from 25 to 600 millivolts of power.
Piezio - a spark producing device often used to ignite gas pilots and burners.
Gas Valves Types:
A. Single Thermocouple Only - Used on some gas logs
B. Valves with Thermocouples and Thermopiles - Used on most hearth appliances and gas logs with switches or remote controls or thermostats.
C. ODS Systems - Used on Mostly Vent-Free. Available in manual control or thermostat/remote/switch (combination) valves.
valvepict.jpg
Typical Gas Valve A. Thermocouple-Only
Found in: Most gas log sets with standard safety pilot knob control. Also found in certain gas space heaters and construction-site portable heaters.
Explanation: This type of gas valve used a single thermocouple. A thermocouple is a device made of two different metals which creates a small electrical charge when heated at one end by the gas pilot. This small charge causes an electromagnet inside the gas valve to open and allow gas to flow to the main burners. Since the thermocouple must be heated before the burner will start, gas appliances often have a startup mode, during which a knob must be depressed and held for 30 seconds or so after lighting the pilot. At the end of the 30 seconds, the pilot should be generating enough electricity for the valve to operate correctly. At this time, the startup knob can be released and the valve turned to an "on" position for appliance operation.
pilotclose.gif Troubleshooting:
Most problems with this type of valve are due to thermocouple problems. Check the following:
1. Connection from the thermocouple to the valve. Clean the threads of the connecting nut with a pencil eraser and re-tighten.
2. Pilot hood and flame direction. The pilot should engulf the top 5/8" of the thermocouple with a decent flame. If the flame hits the thermocouple too low, this can cause the appliance to go out or not generate enough millivolts for valve operation. The pilot hood and orifice should also be clean from soot which could slow or block the pilot flame.
3. Pilot pressure. Many of these valves have an adjustment screw to adjust the pilot flame. A pilot that is too short may allow the pilot to stay lit after ignition, but may not create enough charge to allow the burners to ignite.
4. Overheating: If the unit works for a few hours and then shuts down, it's possible the thermocouple has become overheated. Repositioning of the gas valve and/or pilot may be needed to avoid this problem.
Problems with LP units can also be due to a tank that is nearly empty or a bad regulator at the tank.
B. Thermocouple & Thermopile valve
gas1.gif Found in: Most modern VENTED gas stoves, fireplaces and fireplace inserts as well as vented gas log sets with thermostat or remote control.
This valve is similar to the thermocouple only valve, however has a pilot which heats up BOTH a thermocouple and a thermopile. The thermocouple still acts to prove that the pilot flame is on and allows this flame to continue after startup. The thermopile is used to power a second circuit which is used to open the main valve. This second circuit is powerful enough (300-600 millivolts) to allow the use of a thermostat, wall switch or control switch to operate the main valve. Control of the valve is obtained simply by hooking a pair of wires to two terminals located on the valve.
Startup is similar to the thermocouple-only valve. A piezo spark ignition is used to ignite the pilot after the gas knob is turned to the "pilot" position and depressed. Once the pilot is lit, the knob is held in for 30 seconds to "prove" the heat and then released and turned from the "pilot" to the "on" position. The main burner will then respond to the switch, thermostat or remote control.
Troubleshooting
Since there is both a thermocouple and thermopile in this valve type, it is important to isolate where the potential problem may be. If the pilot can be lit and stays on after the knob is released, then the problem is probably with the thermopile side of the valve. Here are the most common problems and solutions.
1. Pilot does not light or stay lit after knob is released - Make certain that the Piezo igniter works by checking for a spark between the igniter tip and the pilot hood. If there is no spark, the piezo may be bad or the piezo wire might be shorting to the appliance chassis. It is also possible that the igniter tip needs to be bent slightly toward the pilot hood so the spark jumps to it.
Check carefully that gas to appliance is on and that the valve is in he correct (pilot) position and fully depressed when lighting.
If pilot ignites but does not stay lit after knob is released, then the problem is with the thermocouple not generating enough voltage to the valve. It may be that the pilot adjustment needs to be turned up, or the thermocouple replaced. Another possibility is that the thermocouple may not be being "bathed" fully by the pilot flame. Check your owners manual for a diagram and description of the proper pilot flame and hood adjustment. It is also possible that there is soot or other blockage in the pilot tube, orifice or hood which is reducing the size of the pilot (and also the voltage of the thermocouple).
2. Pilot stays lit, but appliance will not turn on - There are two common causes for this. It is possible that the thermopile is not producing enough millivolts to power the control circuit. The millivolts can be checked with a simple voltmeter (consult the owners manual for proper setting) and adjusted with the pilot adjustment screw. Improper millivolts will also cause the appliance to shut down in the middle of operation.
Another common problem is loose or poor connections or circuits to your appliance switch, thermostat or remote transceiver. This can be isolated by simply using a small piece of wire to jump the "TP" and "TH" terminals located on these valves. If the appliance turns on when these terminals are jumped, then you can be sure that your problem is not in the appliance itself, but further down the switch circuit. Make certain you have used the suggested gauge of wire and that the length for your control runs does not exceed the specs given in your manual.
3. Other possible problems - include wind or back drafts affecting the pilot flame and checking of "spillage" circuits which may be wired into the valve in most B-Vent units.
If all the above checks out, and your valve is still acting weird (i.e., works some of the time), then you may have a defective gas valve in the appliance. Problems with LP units can also be due to a tank that is nearly empty or a bad regulator at the tank.
C. ODS System
Found in: Unvented (Ventless, Vent free) gas logs, fireplaces and stoves. These systems are available in manual or remote control.
ods.gif ODS stands for "Oxygen Depletion Sensor" , a term which accurately describes this valve type. The valve itself is similar in many ways to the two valve types above...with one exception. The pilot tube is a precision mechanism that creates a very stable flame as long as the room air contains the proper amount of oxygen. If the oxygen level in the room air drops even slightly, the pilot becomes unstable and lifts off of the thermocouple (see diagram) causing the gas valve and appliance to cease operation. This type of valve is very reliable, and there have been very few failures of this system - even with tens of millions in use worldwide.
0helpful
1answer

I can not use my remote control... i have tried to reset it by pressing the learn button... but not sure what im doing...

If you followed the Owner's Manual Instructions and it didn't beep twice, it may be that you didn't have the slide switch on the transceiver box is in the remote position. Also, the pilot has to be burning for the remote to work. As the heat of the pilot flame against the thermopile generates millivolts of electricity to open or close the gas control valve when the remote control tells it to .Also, be sure that you've turned the Control Valve Knob from the Pilot position to the ON position. In addition, if the thermopile on your gas log set is not generating a minimum of 450 millivolts it won't work. You may want to check the owners manual of your gas log burner to see what it says about the thermopile voltage for that particular burner. And finally, make sure the 12 volt battery in the hand-held is not weak or dead.
3helpful
1answer

Pilot on logs won't stay lit

Hold pilot button longer. if this doesn't work your Thermopile has gone bad and will not generate enough Millivolts to keep gas valve pilot open. A new thermopile will generate 750 millivolts. It cost less than $20 dollars but is difficult to replace. You should call a certified technician. They will charge you about $100.00
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