BD Wait propane wall furnace

Reply

  #1  
Old 12-02-20, 05:35 AM
C
Member
Thread Starter
Join Date: Dec 2020
Posts: 6
Received 0 Votes on 0 Posts
BD Wait propane wall furnace

I have an old BD Wait propane furnace that I want to get going and use. It is in good shape but the PO had unhooked the wires for a reno he was doing. Is anyone familiar with these furnaces? They are very simple, which is what I like about it. It seems to be simply a gas valve, blower, and a thermostat but not sure if anything else is required for it. At present the pilot lights and will stay lit but it will not start. Thermocouple? That seems to be the only safety device on the furnace at all, no circuit board or nothing else. very old school.
 
  #2  
Old 12-02-20, 08:28 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,936
Received 1,351 Votes on 1,249 Posts
Welcome to the forums.

If it only has one device that sits in the flame it will be a thermopile. It generates power to hold the pilot on and light the main burner. Many heaters have two devices. They additionally have a thermocouple that keeps the pilot lit.

I need a model number or some pictures to help with the wiring...... How-to-insert-pictures.
 
  #3  
Old 12-02-20, 08:42 AM
C
Member
Thread Starter
Join Date: Dec 2020
Posts: 6
Received 0 Votes on 0 Posts
Firstly, thank you for taking the time to help me, All I know is it is a BD Wait model CM-600-S
It has 3 wiring contacts on the gas valve, one of them has a red from the valve itself (not sure what it is) the other two have the thermopile/couple wired to them. The thermostat has two wires one to the contact with the thermo on it and the other to the contact with the red wire. i am sure that the thermo is wired correctly as it looks like it has never been removed but the thermostat I am not so sure. The thermostat has no other wires to it so it acts like an on/off switch and no more than that. There is just a blower fan and it is independently wired with a flame or heat detector that I would guess tells the fan when to turn on. I don't know if that works with heat or just "sees" the flame of the burner. My next move will be to change the thermocouple/pile as soon as I figure out which it is. I like the furnace because it is simple and hopefully when I figure it out it will provide heat every once in awhile if needed. There are no other switches or safety devices anywhere on the unit. If the gas valve works it should work? I can take pictures if you need them, no problem there.
 
  #4  
Old 12-02-20, 10:00 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,936
Received 1,351 Votes on 1,249 Posts
BD Wait was built in Canada. Not likely to find much technical info.

A thermocouple connects to a gas valve with a small brass nut.
A thermopile connects to a gas valve with two wires.
Your heater will at least have a thermopile and may also have a thermocouple.



This diagram shows the gas valve as used in a fireplace. Same difference as yours.
There is a loop from TH/TP to TH. The thermostat and any safeties will be in this circuit.

Once the pilot is lit.... check the voltage on TH/TP and TP. You should measure better than 400mv.

Set the t'stat to heat..... remeasure that voltage. What did it drop to ?

Now check from TP to TH...... this should be the same as. If it's much lower you have a poor connection in the safety/thermostat line.

 

Last edited by PJmax; 12-02-20 at 05:33 PM. Reason: whoops - typo
  #5  
Old 12-02-20, 12:32 PM
C
Member
Thread Starter
Join Date: Dec 2020
Posts: 6
Received 0 Votes on 0 Posts
That is helpful, I took a few pictures so you can see what I actually have. I tested the thermopile and all I get is 2.4 mV when heating it up, guessing that is where to start. See pictures attached please.
1. mV reading when heating 2. Gas Valve, I have marked how it was wired
2. Blower set up, (what is the "eye" called on top?) 3. Thermopile and pilot set up



4. mV reading when heated with torch



 
  #6  
Old 12-02-20, 02:09 PM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 24,478
Received 755 Votes on 694 Posts
You need to set your meter to DC (not AC) to test the thermopile. Make sure it's wires are not connected to anything when you test. A new one should be around 750 mv and they loose power as they age. When they get down around 450 mv is when I start to see problems and by 400 mv there isn't enough to open most gas valves.

Also, millivolt systems need very good electrical connections. With such low voltage even the tiniest bit of corrosion on electrical contacts can prevent it from working.
 
  #7  
Old 12-02-20, 02:11 PM
C
Member
Thread Starter
Join Date: Dec 2020
Posts: 6
Received 0 Votes on 0 Posts
OK, I thought I read AC mV somewhere but DC makes sense. I will retest.
 
  #8  
Old 12-02-20, 03:55 PM
C
Member
Thread Starter
Join Date: Dec 2020
Posts: 6
Received 0 Votes on 0 Posts
I retested it on DC mV's It will get to 400+ but seems to take a long time. Also the meter will automatically switch from mV to V after 400 and go to the V .000 scale. I figure that is normal maybe? I think I will replace it to be sure and clean up the contacts on the valve and see what happens.
 
  #9  
Old 12-02-20, 05:36 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,936
Received 1,351 Votes on 1,249 Posts
It never hurts to replace the thermopile. However..... the pilot flame is just as important. The thermopile must be well engulfed in a hearty flame. A typical problem is a partially plugged orifice. In my previous diagram.... the red arrow is pointing to where the orifice is usually located.
 
  #10  
Old 12-03-20, 05:42 AM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 24,478
Received 755 Votes on 694 Posts
In a modern appliance the pilot light and thermopile functions as an oxygen depletion sensor to turn the appliance off if the oxygen level in the room drops too low. The orifice of the pilot is a calibrated size to make a flame of a specific size. When there is less oxygen the flame is weaker which makes less heat and the thermopile no longer makes enough electricity to hold the gas valve open. You can clean the orifice but don't use a drill bit or reamer. Nothing that will take off metal and make the orifice larger.
 
  #11  
Old 12-05-20, 07:08 AM
C
Member
Thread Starter
Join Date: Dec 2020
Posts: 6
Received 0 Votes on 0 Posts
Good news, I was able to get the furnace on. I replaced the thermopile and adjusted the pilot so it was more evenly directed at said pile. May have been a poor connection as well. Now if I could understand what controls the fan I would be all set. I could wire it direct I suppose but it would be good to have things work as they were intended. I donít know what controls the fan or what it is even called to research. It is in one of the pictures. Any idea ? Thanks again for your help
 
  #12  
Old 12-09-20, 09:01 AM
S
Member
Join Date: Jan 2017
Location: USA
Posts: 547
Received 5 Votes on 5 Posts
The fan is usually powered on by a temperature sensor which is usually mounted near the top of the air flow. that switches line voltage on/off
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description: