Thermostat wiring for gas wall heater ?


  #1  
Old 02-02-07, 03:15 PM
L
Member
Thread Starter
Join Date: Feb 2007
Location: Abilene
Posts: 3
Upvotes: 0
Received 0 Upvotes on 0 Posts
Smile Thermostat wiring for gas wall heater ?

In our garage apartment, there is a wall-mounted heater that is the source of heat.

It is not working, and I have removed the olde thermostat controller in order to replace it. There were two wires running to it. I replaced it, but it still does not work. I am told that there is supposed to be a 24 volt transformer providing power. Well, I cannot find it anywhere, nor can I find any other wires. The only wires going to ther gas valve are the two thermocouple wires and the two wires for the thermostat. Clearly, something is missing....

I can make the heater work fine by running 3 volts dc between the two thermostat wires, but of course, we want an effective thermostat. What is the wireing plan for a typical wall mounted spave heater?


Thanks in advance ~ ~ Logger
 
  #2  
Old 02-02-07, 05:22 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Thermostat

I suspect you need a thermostat which will operate a millivolt system. Many of the gas wall mounted heaters have a small device which sticks in the pilot flame to generate a millivolt current, usually between 100 & 750 millivolts.
 
  #3  
Old 02-03-07, 06:09 AM
H
Member
Join Date: Jul 2005
Location: New York
Posts: 657
Upvotes: 0
Received 0 Upvotes on 0 Posts
From your description, there is nothing missing. As Grady said, you have a millivolt system on that heater and will need a thermostat specifically for it.

The thermopile should be connected to the "TP" and "TH/TP" connections of the gas control valve. The thermostat leads should be connected to the "TH/TP" and the "TH" terminals of the gas control valve.

While the pilot is lit, take a reading with a multimeter at the TP and TH/TP terminals. You should get about 400 to 450 millivolts. Once you turn the thermostat on, it should drop to about 200 millivolts.

If you get these readings and the furnace still doesn't light, you can jump the "TH/TP" and the "TH" terminals out. If the furnace ignites, then you either have a bad thermostat or bad thermostat wires. You can also check for continuity in the thermostat wires with the thermostat on.

Do not use an outside power source (battery or transformer) to fire the unit. In doing so you will likely damage the gas valve and possibly create an unsafe situation by letting gas flow when there is no pilot.
 
  #4  
Old 02-03-07, 11:47 AM
L
Member
Thread Starter
Join Date: Feb 2007
Location: Abilene
Posts: 3
Upvotes: 0
Received 0 Upvotes on 0 Posts
Red face Problem solved - Thanks Grady & HankHill 6018 . . .

I had already installed a new thermostat, with no luck - it turns out that the thermostat was not the problem.

First off, Grady, thanks for letting me know that there are two different systems - I was about to wire in a 24v transformer - which would not have solved the problem.


HankHill, when you gave me the thermopile voltages to look for, I measured and got only 230 mv with no load (in the 'Pilot mode) and 155 mv in 'On mode' with the wires clip-leaded together. Hmmm . . . . inadequate voltage - AHA !!!! I opened the pilot adjustment cap and turned the pilot light up, raising the voltage to 400 mv in the process. The heater roared to life.

Of course, the flames went out when I removed the clip-lead frpm across TH/TP & TH terminals. Realizing soon that I would never be able to make a 24v thermostat work, I put the olde, ugly mercury thermostat back on.

Works like a charm!! Apparently, the thermopile was getting weak.


Thanks again, fellas ~~
 
  #5  
Old 02-03-07, 03:26 PM
H
Member
Join Date: Jul 2005
Location: New York
Posts: 657
Upvotes: 0
Received 0 Upvotes on 0 Posts
I'm glad it all worked out.
 
  #6  
Old 11-03-13, 05:49 PM
K
Member
Join Date: Nov 2013
Location: United States
Posts: 1
Upvotes: 0
Received 0 Upvotes on 0 Posts
OK but what is wrong if you cross the wires and the burner doesn't light. Kenfro
 
  #7  
Old 11-03-13, 05:55 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Have you checked any voltages as described above? If not you need to do so & report those votages here. After that we might be able to help.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: