Hi All,
I have a 5 y/o 80% eff bryant furnace. The problem I have is that my furnace
Doesn't always kick on even when thew thermostat shows the temp under the
Temp set. I will sometimes have to go down and turn of the blower switch on the furnace wait a couple seconds and then turn it on again. It will start the furnace
And it will heat up to just under the temp set and then shut off again. Example:
The other day the Thermostat showed 62 deg but the furnace was set at 69 and
The furnace did not come on. I went down and flipped the fan switch off, waited
20 sec and turned it back on, it started up and ran till the house was warm.
Someone told me it was the blower limit switch? I don't know a lot about furnaces
But I would like to fix it myself, but I don't want to replace part after part till it is fixed.
So if anyone with experience knows what might be wrong I would really appreciate
The help. Thanks

Henry

When you say that you turn the fan switch off - is the fan switch located on the furance or is it located elsewhere?

Hi lotta,
The switch is mounted on the outside case of the furnace. It looks like a light switch.
If you switch it off the fan will not blow. This is why my friend said it was a
Blower limit switch. I have a basic digital thermostat, Heat/Cool - ON/OFF
Not programmable. Any help would be appreciated. Thanks

Henry

I have a 10 year old Bryant likely much like yours except no external blower switch. Can't understand the purpose of such a switch. Are you sure it isn't a power switch? Does your furnace have a red light showing it has power? Does it go out when you turn the switch to off?

Unless the wiring to the blower was messed up when the switch was added, likely the problem is on the control board. It has a timer that should activate the relay controlling the blower a minute or 2 after the gas comes on. Problems on the control board are difficult to find and fix. Unfortunately paying for a control board is difficult too, I paid about $300 for one.

Older furnaces use a limit switch to control the blower, but mostly timers now. There are temperature sensors in the furnace, but they shut the gas off if it fails to ignite or the blower fails to come on.

Unless you can find a problem in the wiring to that switch, likely you will have to replace the control board. No big job if you can remove about 10 wires and plugs and get them back where they belong. Note the thermostat wire, red on R, white on W, etc. I hate to say replace an expensive board without being sure it is the problem. The other alternative is to pay a technician another $100 to do it.

Will the blower come on if you select On? If so, you may be able to run the furnace that way, buying you time to order a board over the net.

Ive seen poor grounding are a loose nuetral make a newer gas furnace with a control board in it do some strange things. You may want to check your grounding and neutral at the panel and at that switch

I have a very similar problem with my Bryant Furnace, when the problem occurs, the blower will stay on and the red light will be flashing. To solve the problem I will shut the Thermostat switch to the off position, and then check the red light; if the light is not flashing I will wait a couple of minutes then put the Thermostat switch back to the "heat" position. If the red light is still flashing I will shut the system down by the main power switch (the switch that looks like a wall light switch). I also noticed problems where the heat would kick on then 5 seconds later shut down, when this happens the main blower stays on and the red light would be flashing. I would also like to know why this problem occurs and how it can be fixed. Labman seems to have the best answer to the problem, and I believe what tombstoner refers to the external blower switch is actually the main power switch.

Hello Labman and Matureman,
I have a 9yr old Bryant with the same power switch mounted on the outside. I am currently having similar problems where the fan blows but no heat. I cycled the power switch mounted on the outside and eventually it started in about 8 minutes. I can hear the furnace ignite and then shut off several times before success.
Has anyone figured the problem out yet?

First... the switch you are referring to is a Service Switch. It's required by many local codes to shut power off to the furnace when working on it. The reason the fan shuts off... well you get the picture.

Second. Shutting off the furnace is simply clearing the error from the memory of the board, and resetting the board-it is not a repair or remedy.

The flashing red lights are Diagnostic Codes for the furnace, and the codes are listed inside the outer door. Count the slow and long flashes and refer to the code, and it will tell you what the problem is. Continuing to reset the unit will only result in delayed (and possibly additional) repairs.

Check/Change filter. Do this before ANYTHING else. If it's packed, remove it and run unit until a new filter gets there-no more than 2 days.

Reset the furnace 1 time, watch the sequence of operation (inducer motor, glowing ignitor, main burner, fan). Chances are that there are leaves stuck in the intake of the furnace and it's failing on the pressure switch OR the hot surface ignitor is bad (look for glow 30 seconds or so after little motor/inducer comes on). If it's pressure, disconnect the PVC pipe from the burner housing and remove the leaves from the intake. Then put some screen or chicken wire around the intake outside the home to prevent recurrence. If it's a hot surface ignitor (unplug ignitor and check for 120v approx 30 seconds after inducer starts), you will only be able to get one from an A/C supply house or a mechanic.

Beyond these 2 errors, I recommend calling a professional.



Good Luck!

Hello Labman and Matureman,
I have a 9yr old Bryant with the same power switch mounted on the outside. I am currently having simalar problems where the fan blows but no heat. I cycled the power switch mounted on the outside and eventually it started in about 8 minutes. I can hear the furnace ignite and then shut off several times before success.
has anyone figured the problem out yet?

Pull and clean flame sensor (little metal rod on bottom left of burner compartment) held in by 1 1/4 inch screw. Remove screw, let it gently drop down-don't chip the porcelain-and clean it with double ought steel wool (you can generally find it at NAPA). Do not touch metal, do not chip porcelain, and reinsert it and restart furnace. This should clear up the problem.

Good luck!

I also noticed problems where the heat would kick on then 5 seconds later shut down, when this happens the main blower stays on and the red light would be flashing. I would also like to know why this problem occurs and how it can be fixed.

See the post regarding "cleaning the flame sensor". Hope this helps.

I can't answer the question but I have a similar problem to the original posting. I've been trying to troubleshoot my problem but w/ no success. Evertime I think I have a solution it doesn't work. My furnace function properly sometimes for up to a couple weeks and then I find it in a fault mode. I think its 1 then 3. The following is what I do. I turn off then on the service switch. Main blower kicks on for XX seconds. Exhaust blower kicks on then... comes the strange part. Sometimes everything works fine and continues cycle and no problems for usually a few days/weeks. The other times when it doesn't work is where it gets strange. The blower motor will stop and no ignitor and it goes into fault BUT if I give the main contol board a little knock (sometimes 2 or 3) the exhaust blower will continue and the rest of the cycle will continue. It's good again for a few days/weeks. I have taken off all the wires to the conrol board and cleaned them. I've tried to wiggle them one by one to see if one is causing the problem but... no luck. The real question is... Should I break down and buy the $300 control board?

If you have a fault code the furnace is shutting down for a reason. If you have a bryant code 13 is limit lock out. Its hard to tell you need to start a new post, this question was from 2005. Give as much info as you can good luck.

Once again... clean the flame sensor. Many times, when the furnace acts the way you are describing, it is a dirty flame sensor (or defective one).

Bryant plus 80 unit, my blower w/not come on, w/heat or air. I put a capacitor on and new filter. Furnace ignites but fan never comes on, no heat.

I have a question I have someone looking at my furnace he told me it was my control board so got one and he put it in no lights or anything is coming on but my board coming into it is showing it is getting 115 volts help please

My furnace is a rheem classic 90s plus made in 2002

Hi, my problem is the same. The thermostat is set at 69, it gets down to 60 or 61 and blows out cold air. Eventually we turn the switch off and back on again, and it stsrts over again. Any sugestions?

If blower keep running with the burners off you got to check high temp limit switch

The furnace comes on ,but it does not reach the temperature set on the thermostate before shutiing down example if I set it on 80 it goes to g65 and shuts down . When it shuts down if I jump the two wires in the thermostate the furnace will start . I do this to check the thermostate . I think the digital thermostate is bad

I have a 20 year bryant furnace model sx242nbox and the pilot light knob is stuck on, I am trying to re light it because the gas company had to turn our gas off and its stuck, I cannot move it to off or pilot. Please help someone

We just replaced our thermostat and now our furnace won't kick on. The furnace code is telling a secondary voltage fuse is open. Is that the breaker in our fuse box?

Thank you