Flame On/ Flame off!


  #1  
Old 01-05-03, 06:25 PM
JJordan
Visiting Guest
Posts: n/a
Thumbs down Flame On/ Flame off!

I have a Comfortmaker (model FBF050B12A2) that quit a few weeks ago. The draft inducer motor was making a humming sound and I got it to start by turning off the power via breaker and then turning it on again. The motor must have been stuck or something. The repair tech that checked it out the next morning said that the draft inducer was on it's way out. The body was extremely hot even when it ran for a short period, so I assume that this aided his diagnosis. I ordered a new one and plan to attempt the install myself. Anyway, since that time, I have noticed that the burners turn off, then there is a clicking sound (I assume that it is the ignitors) then the flame fires up again and continues to heat. All the while the fan that forces the air past the heat exchanger never quits. It ususally does this two or three times during the heat cycle. What causes this? Could it be the faulty draft inducer motor? And the second question, how difficult is it to replace the draft inducer assy?

Thanks for any help you might render.

Regards,

Jeff
 
  #2  
Old 01-05-03, 06:53 PM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 10,237
Received 66 Upvotes on 61 Posts
JJordan:

There is a possibility that the inducer motor is not running at full speed and the heat exchanger is overheating.

Inducer motor should be an easy job.
 
  #3  
Old 01-07-03, 10:58 AM
JJordan
Visiting Guest
Posts: n/a
Question Hard Starting Gas Furnace

My Comfortmaker FBF050 model needed a new draft inducer motor as the orignal was beginning to make noise. So I replaced it which wasn't as hard as my mind made me think it would be. NOW the when the tstat calls for heat, the inducer motor starts, the unit clicks, the main burners ignite, then they shut off, then it does this cycle (click, main burner fires, shuts off) for about 3-four times, then functions normally. All the while, the draft inducer motor is running normally. I have checked the hose from the inducer to the pressure switch and that seems intact. What's going on with the thing? I thought I was doing myself a favor by replacing the inducer motor before it went south, but it seems that I have caused more problems. Please help as this is driving me CRAZY!
 
  #4  
Old 01-07-03, 06:14 PM
bigjohn
Visiting Guest
Posts: n/a
Todays furnaces are much more complicated than those of a generation ago and there are simply more things to go wrong. Most likely, the flame proving/verifying circuit is intermittent. These systems work on the principle of a current being conducted thru the flame to ground. Anything that interrupts that circuit, [loose connections, corrosion] will cause the burners to shut down and recycle. It sounds like you're saying that the furnace has a spark igniter? Take it out, clean the flame rod with some steel wool or the like, clean the surface where the bracket mounts and the underside of the bracket. Check all ground connections both inside the furnace and all the way back to the circuit breaker panel. You can also look thru the postings for the past couple weeks as we've extensively covered this topic. Check these items out and let us know what happens.
 
  #5  
Old 01-08-03, 05:19 AM
JJordan
Visiting Guest
Posts: n/a
Thanks guys! I did all of those things with the exception of cleaning the "flame rod" as I don't have clue as to what that is. I cleaned all of the ground connections too. The only thing that changed is that I made it worse! Now the burners fire up for 15 seconds, cycle, fire up for another 15 or 20 and repeats this sequence for about two minutes. Then finally they stay burning and we are good to go (until next time). The funny thing is that last night, sometimes it didn't do this and it operated normally! This is killing me! What next?
 
  #6  
Old 01-08-03, 02:10 PM
bigjohn
Visiting Guest
Posts: n/a
At this point we need a tad more information to work with. What lites the burners? Does the furnace have a sparker that lites a pilot flame or does it have a Hot Surface Igniter? [a glow coil] It sound like you have an HSI system. They come in 2 flavors. One where the flame rod is built into the igniter and the other where the flame rod is separate from the igniter. Locate the module and post the brand and model #.
 
  #7  
Old 01-08-03, 06:03 PM
JJordan
Visiting Guest
Posts: n/a
It's the kind that acts like a sparker to ignite the pilot then acts as a flame sensor...all in one rod. It is made by Honeywell and carries Comfortmaker part number 1011483. I know what I'd like to call this system...and it's unfit to type and post! Thanks for all your help. It's getting cold upstairs.
 
  #8  
Old 01-08-03, 07:40 PM
bigjohn
Visiting Guest
Posts: n/a
That single rod you see, that's the flame rod and igniter. Try cleaning it with some steel wool or the like. They can get an oxidation buildup. Look closely at the ceramic insulator with a magnifying glass. If it looks like there are any cracks, replace the whole asssembly. [if the module is HW, the burner/igniter is probably also HW] Are you sure you took the assembly out and cleaned the mounting point and the underside of the bracket where it contacts the burner? What does the cable going to the igniter look like? It's not laying against any metal? How about the connecters on both ends? Usually, intermittent operation is something interfering with the flame sensing circuitry [read poor grounding, corrosion, poor connections, etc.] or a squirrelly module. HW modules are pretty reliable.That, plus modules are expensive and I prefer to exhaust all possibilties before condeming a module.
 
  #9  
Old 01-09-03, 04:36 AM
JJordan
Visiting Guest
Posts: n/a
Bigjohn:

I actually procured a NEW ignitor/sensing rod and replaced it. It continues the same old thing. I am not real happy with they ground the module that this thing plugs into (I assume that is some sort of computerized curicuit board). Shoud I run a separte ground wire from the module to the main ground coming from the home wiring? Thanks for the help. Not too cold last night as we are having a mid winter "warm spell."

Thanks.

JJ
 
  #10  
Old 01-09-03, 08:50 AM
bigjohn
Visiting Guest
Posts: n/a
When the burners cycle off, does the inducer motor stop or does it keep running. When the burners cycle off prematurely, see if your're losing the voltage input from the combustion air flow sensing switch to the module.
 
  #11  
Old 01-09-03, 09:17 AM
JJordan
Visiting Guest
Posts: n/a
The draft inducer keeps running. It takes several of these cycles to heat up the heat exchanger to the point that the forced air motor begins. But once this happens, the burners keep burning until the tsat tells the unit to shut down as the room has reached temp. When they are buring, and I remove vaccuum (take the hose loose) from the pressure switch, the burners quit. So I assume that switch is functioning properly. Is this switch the combustion air sensing switch. The one that I tested has a tube from the draft inducer to the switch.
 
  #12  
Old 01-09-03, 02:00 PM
bigjohn
Visiting Guest
Posts: n/a
Yes, that's the combstion air flow sensing switch. Should be round and look like it has a diaphragm inside. An extra ground wire an't hurt. The cable that goes from the module to the igniter, what kind of shaoe is it in? Make sure it's not laying on the metal parts of the furnace where it could be leaking the feedback sihnal to ground. Go to the thermostat and move the FAN switch to ON so that the forced air motor runs full time and then turn on the heat and see what happens. What configuration is the furnace? Upflow, Downflow or Horizantal?
 
  #13  
Old 01-10-03, 07:21 AM
JJordan
Visiting Guest
Posts: n/a
It's an updraft kind I think. Still cycles with the fan switch to ON vice AUTO.

Well, I declared all out war on this heater. I have replaced the combustion flow sensing switch, the ignition module and the ignitor/flame sensor. I am going to route the blue wire (new on the flame sensor) away from all metal objects and tie it to other wires tonight and see if that makes a difference. Didn't have time to test it out this morning before going to work, but I did notice on the comb flow sens switch (pressure switch) that it had some black on one of the terminals, like it had arced at one time. WOnder if this could cause the switch to act intermittently? How 'bout that circuit board looking thing in the bottom of the heater? I think that controls to fan motor, but not sure. About the only thing I haven't replaced in this piece of XXXXXX is that circuit board and the gas valve!
 
  #14  
Old 01-10-03, 01:32 PM
bigjohn
Visiting Guest
Posts: n/a
The circuit board is probably the fan timer board. Intermittent problems will drive you nutso because you have to catch it in the act in order to make a confident diagnosis and repair. I'm curious to know what happens. Thanks.
 
  #15  
Old 01-10-03, 05:42 PM
JJordan
Visiting Guest
Posts: n/a
BigJohn:

Well I am happy to say that I WON the war over Comfortmaker. After replacing all those parts, I noticed that the pilot light was kinda like being blown out. I didn't know that the PL needed to burn to keep the burners going. I thought that it was needed for ignition only, then wasn't needed. duhhh! Anyway, it seems that when I changed the ignition/flame sensor unit, I used the old orifice from the old unit rather than using the orifice supplied with the new unit. I changed to the new supplied orifice and bingo, the pilot remained lit and the burners burned without cycling. Apparently the flame was not strong enough to keep going with the new draft inducer. I figure since the old inducer was running under speed (bearings going out) that the draft was less and therefore didn't blow the pilot out. With the new motor running full speed, it blew the pilot out sometimes and sometimes not. Anyway, it is corrected for now I hope. The moral of the story is:

THEY PUT NEW PARTS IN THE BOX FOR A REASON...USE THEM!!!

Thanks for all your help. You and this forum are great. I have learned so much about gas fired furnaces in the last few days. Thanks again.

Jeff
 
  #16  
Old 01-10-03, 08:19 PM
bigjohn
Visiting Guest
Posts: n/a
Yeah buddy- if u didn't need those parts, they wouldn't be there. The pilot flame has to stay lit in order to keep the flame proving circuit active. You have to mull the concept over in your mind the way a cow chews her cud. The pilot flame is conducting electricity like a wire would EXCEPT it rectifies [changes] the current flow from Alternating Current to a pulsating Direct Current with a microampere flow of current. [hence the name- flame rectification] Shut off the pilot and you turn off the circuit that verifies the pilot flame and the module shuts the burners down. I'm glad your heat is back on. Next time your furnace acts up, you'll have a better idea of what to look for.
 
 

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