Gas Furnace Problem

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  #1  
Old 11-24-02, 12:18 AM
Sheri E
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Unhappy Pilot Lit But No Heat

Hi all,

I have an old central heating system with a standing pilot. The pilot is lit, but I'm not getting any heat through the vents. When I turn on the thermostat, there is no sound of the main burner lighting. Brrrr!
 
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  #2  
Old 11-24-02, 07:05 AM
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Unhappy problem with the heat

Measure the voltage on the gas valve. Put the black probe to ground and dont move it till we get to the transformer, the red lead to M. you should have 24V, if not, then the valve is not suspect, move the red probe to the 24v terminal on the igntion module, this is sometimes labeled TH, if 24VAC is there, the module is bad, if not, then you have no signal from the thermostat, or the rollout switch is open. Some use a rollout switch , some use a fuseable link. Check with the red probe probing both sides of the rollout switch. Both sides should have 24VAC. If one side does, and one side dosen't, the switch is open. If no 24V on either side, check the transformer for 24VAC (usually yellow and blue) use both probes here. make sure your on the secondary sideof the transformer, the other side is line voltage(120VAC).
The path for the voltage is thermostat, safetys, (rollout, high limit,...) ignition module gas valve. Try that !
 
  #3  
Old 11-24-02, 07:47 AM
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Several Possibilities

Hello Sheri E. Welcome to the Heating & Cooling forum & our Do-It-Yourself Web Site.

If there is electrical current to the furnace, that eliminates at least one possibility. There could be many possibilities which would need to be determined. Too many to list here in a single reply or multiple replies by several heating professionals.

However, there is a vast number of prior questions and many replies within each of them on this subject of gas furnaces already posted. Check both the "Gas Appliances" topic and within this "Heating & Cooling" forum for all the possibilities & possible solutions. In doing so you will find the solution.

First item to check is the thermostat. You'll need to remove it from the wall, disconnect the red and white wires from it. Then connect only the red and white wires together. If the heater operates, thermostat is defective.

If the heater still does not operate, either the thermostat isn't getting current or current isn't getting to the thermostat from the low voltage transformer. You'll need to check for voltage at from the 2 wires. The amount of voltage is not important. Just that current is there.

Possible the gas valve or the safety isn't working. Possible the "Pilot Generator" or "Thermocouple" isn't producing current, depending upon which safety system the heater is equipped with.
For additional problem possibilities and repair solutions, read the recent postings within this forum pertaining to heater topics. The questions already asked describe like or similarly related problem descriptions as your question.

These prior postings and any or all the replies offered within them contain almost all the required information needed pertaining to the many potential and or possible problems with the heating unit like your describing.

An excellent source for original replacement parts is your local retail appliance parts store, the local heating dealers and agents retail part stores. Bring the make, model and serial numbers. The info will help to determine the possible problem causes.

Heating Agents & Appliance part stores carry replacement parts for almost every heater brand. The locations for the dealers, agents and retail part stores are listed in the phone book.

Resident heating professionals replying within this forum, may have alternate solutions, suggestions, opinions and or test and repair methods. Check back several times for additional replies.

If you need further assistance, use the REPLY button to add any additional information or ask additional questions after attempting the correctional method or methods offered.

Regards & Good Luck, Forum Host & Multiple Topic Moderator.
TCB4U2B2B Company Enterprises. Energy Conservation Consultant & Gas Appliance Diagnostics Technician.
 
  #4  
Old 11-24-02, 11:51 AM
Sheri E
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Thanks to the both of you. I will go through this diagnostic today and update later. Thanks again!
 
  #5  
Old 11-24-02, 03:57 PM
Sheri E
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Re: Several Possibilities

First item to check is the thermostat. You'll need to remove it from the wall, disconnect the red and white wires from it. Then connect only the red and white wires together. If the heater operates, thermostat is defective.
I've removed the thermostat. It's an older model, non-digital. The wires are both white. I'm just checking in to make certain it's OK to touch these two wires together.
 
  #6  
Old 11-24-02, 04:10 PM
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yes

go ahead
 
  #7  
Old 11-24-02, 04:12 PM
Sheri E
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No Dice



So, nothing happened. On to step 2...
 

Last edited by Sheri E; 11-24-02 at 04:33 PM.
  #8  
Old 11-24-02, 04:52 PM
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Hello: Sheri E

At this point we can determine that when the thermostat wires are connected together, nothing happens. You mentioned and old central heating unit with a standing {constantly on} pilot.

Do you notice or see and red reset buttons? Most likely on the gas control valve or attached to the front of the furnace. The point here is to determine if the heater has a "Pilot Generator."

If so equipped, the gas valve would have a tiny "B" shaped valve which can be turned to turn on or off the pilot flame. If the unit has this type of pilot system, the pilot flame remains on regardless of furnace operation or non operation.

Having this type of constant burning pilot flame could mean the furnace has a Thermocouple or Pilot Generator. If so, the pilot remains on but either of the parts, whichever the heater has, is defective.

Replacing either the generator or thermcouple would then be required. Either of these parts will have an element end the pilot flame will be heating. The other end of either of these parts will be connected to the gas valve or a "Basso" valve.

The Basso name will be on the front cover of the valve. It is a seperate part attached to the furnace and not part of the original gas valve. Usually has a chrome metal detachable cover on it.

Good Luck. Forum Host & Multiple Topic Moderator.
TCB4U2B2B Company Enterprises. Energy Conservation Consultant & Gas Appliance Diagnostics Technician.
 
  #9  
Old 11-24-02, 05:15 PM
Sheri E
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If the heater still does not operate, either the thermostat isn't getting current or current isn't getting to the thermostat from the low voltage transformer. You'll need to check for voltage at from the 2 wires. The amount of voltage is not important. Just that current is there.
I used a low voltage reader at the thermostat and the indicator did not light.
 
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Old 11-24-02, 05:19 PM
Sheri E
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Oops

Previous was posted before seeing Tom's latest reply.

When I was last face to face with the furnace, I did notice a mechanism to turn the pilot on and off. I'll check the Basso name right now.
 
  #11  
Old 11-24-02, 05:31 PM
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Sheri E

It is important to do as many tests as possible before posting back the replies. Reasoning is so the progress can continue at a faster rate. The sooner the exact problem can be established, the sooner the furnace will operate.

Have you determined what type of pilot system the heater has from the indications I offered? Doing so would help to determine which type of pilot system and safety system your furnace has.

Once you can determine that we can diagnose some problems associated with those systems. You'll also need to follow & complete all the directions offered by hvac01453.

To help, print the page. The option is in blue link format below. Scroll down this page to "Show Printable Version." Printing the pages may help.
 
  #12  
Old 11-24-02, 05:59 PM
Sheri E
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I'm working on hvac's directions. I don't see anything that is marked "M", as directed here:

Measure the voltage on the gas valve. Put the black probe to ground and dont move it till we get to the transformer, the red lead to M.
I went on to test the ignition module (labeled TH and TP) and no current was found. I don't know what the rollout switch or fuseable link would look like, but I ran the probe over every component on the valve and nowhere was there a current. I followed the path (thermostat to safetys to ignition module, etc.) as best I could and no voltage reading could be found.

From what I can tell, this furnace has a thermocouple. The gas valve label says Robertshaw-Grayson 700 Series for Millivolt.
 

Last edited by Sheri E; 11-24-02 at 09:52 PM.
  #13  
Old 11-24-02, 10:00 PM
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Sheri E

Based on what I think is the age of the furnace, it would not have an ignition module, fuseable link nor a rollout switch. The furnace most likely has a thermocouple.

The element end is being heated by the pilots flame. The other end is screwed into either the gas valve or a safety device. Either of which should have a push in button or lever or pull down ring.

The pull down ring is often referred to as a "D" ring because it looks like a letter "D" It is at the base of the gas valve. Often the D Ring is colored red and encirles a cone shaped upside down tower below the gas valve.

Pulling the D ring down resets the safety. Same applies to pushing in a red button or holding a lever to the reset position for about a minute to reset the safety. Look for pilot liting and resetting instructions on the furnace plate etc.
 
  #14  
Old 11-24-02, 10:39 PM
Sheri E
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What I thought was the ignition module is the wiring block maybe?

I searched the entire thing and no sign of reset button, lever, or D-ring

Another thing, I looked up pictures of thermocouples and they do not match what I have. Mine has two wires that attach to the wiring block with another wire that attaches to the thermocouple connection.
 
  #15  
Old 11-24-02, 11:18 PM
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transformer???

Does it have a low voltage transformer?
Can you see if it has a standing pilot flame and is lit?
 
  #16  
Old 11-24-02, 11:22 PM
Sheri E
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It does not have a transformer.
It is a standing pilot and it is lit.

This is the model that I have:

http://216.239.53.100/search?q=cache...hl=en&ie=UTF-8
 

Last edited by Sheri E; 11-24-02 at 11:41 PM.
  #17  
Old 11-25-02, 11:02 AM
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checks

I think what you might have is a thermopile. Basicly power is generatored by the flame. does it look like a wire coming from what looks to be a fat thermocouple. Thermocouples usually have a copper cappilary tube that screws into the gas valve. Thermopiles generate larger amounts of power (all still under a volt), this may have a small fork connector at its end. ???
 
  #18  
Old 11-25-02, 11:17 AM
Sheri E
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You got it! I think I need to replace it. I opened a new thread about this.
 
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