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Cozy wall furnace model w255d pilot will not stay lit and thermopile has been replaced 750 millivolt system

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Ensure the end of the thermopile is in direct flame, any lower or higher it will not allow the pilot to stay on..

Posted on Dec 04, 2008

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How do you convert a remote thermostat to a directly wired digital thermostat to a vulcan powerhouse 100 central heater unit


First, you need to know how many millivolts the Thermopile (aka Pilot Generator) on the the furnace's pilot assembly millvolt terminal. Then you find a wired digital thermostat, that meets the same millivoltage that the Thermopile Generates or has a lower requirement. You have to run millivolt wiring from the furnace's pilot assembly millivolt terminal block (the wiring should be connect to the TH & the TPH terminals, to where you want to place the digital wall thermostat. In most cases, it can not be more that 15' away from the furnace. In other words, no more than 15' of wiring can be involved.

Hope this helped you. Please let me know. Thanks.

Jun 20, 2011 | Heating & Cooling

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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...


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 angie.parish@lennoxhp.com.

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

Mar 25, 2011 | Heating & Cooling

1 Answer

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.

Mar 02, 2011 | Heating & Cooling

1 Answer

I have been working on a wall mounted furnace. The pilot will not remain lit. Assuming it's the thermalpile but everything seems brand new


New or not,parts go bad.
The thermocouple/thermopile must be in good working order for the pilot to stay lit.

Jan 12, 2011 | Heating & Cooling

1 Answer

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

Oct 19, 2009 | Desa International Wall/Window Air...

1 Answer

Cozy wall heater working intemittently


Sounds like a limit switch is tripping.
This appliance is equipped with a manual reset blocked
flue switch designed to protect against a blocked flue condition,
which would cause combustion products to spill back into the
living quarters. NOTE: A partially blocked, inadequate, or
disconnected vent system may not activate the switch.
Discoloration of the grille is an indication of a bad vent. If this
occurs, the vent can be checked by a qualified serviceman using
a draft gauge. After 15 minutes the gauge should read between
-.02 up to -.04 inches w.c. Vent must be checked at the
beginning of each heating season.

Jan 28, 2009 | Heating & Cooling

1 Answer

I have a Raypak pool heater with a invensys gas valve, the burner is not kicking in, pilot light is lit and stays lit, I jumper the complete switch circuit and still does not kick in. this is a millivolt...


Usually not the gas valve unless line voltage was applied to it. Millivolt systems are very touchy about connections. First check the output of the millivolt generator (thermopile) the wires for this usually go straight to the gas valve they should be one red and one white usually in a high temp fiber glass sheath. The wires will lead from the gas valve to a rod by the pilot. Test between the two wires with a meter that can read mV DC. You should have somewhere in the neighborhood of 450-600mV DC. If you do not, then the thermopile is bad. If you do, then it is either a bad connection somewhere or an open safety in the circuit. Check all of the safety devices and clean all of the connections in the unit with sandpaper. Usually for safety devices there will be a high limit on the discharge of the header, a pressure switch sensing water pressure, and a rollout switch or two in the control compartment above the burner. Good luck, I have to battle with mV systems all the time at work, usually it's just a bad connection.

Thanks,
Chillmaster

Jul 02, 2008 | Heating & Cooling

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