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Heil gas furnace problem

Duckula
Duckula Member Posts: 5
Hello



I am having a problem with my gas furnace. I have a heil model nug9100fha1. 100,000btu. The problem is that the furnace started to run on a call for heat but switched over to ac on the thermostats. I am using a honeywell programmable model chronotherm iii. I thought maybe I was having a control problem so I pulled the thermostat and replaced the batteries. The thermostat will not contol the furnace. The furnace runs non stop. The thermostat does nothing. I had to turn the breaker off to shut down the furnace. No matter what I tried the thermostat will not clear the ac indication on the LCD display. I am thinking after 15 years the thermostat has bit the dust ........maybe not? Can anyone help.



Thanks

Jeff.

Comments

  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    Go to the back plate

    that has the wires attached and disconnect the "Y" and "G" wires leave "C" , "R" and "W" alone put it back together and try it that should be just heat.



    You might also try reprogramming the thermostat.



    Then again you may be right the thermostat may need to be replaced, before you do that have an HVAC technician take a look at it.
  • Duckula
    Duckula Member Posts: 5
    Heil furnace problem

    I was mistaken Tim, the outdoor unit is not running. It seems as though the furnace is trying to go into a heat cycle as the evacuation fan is running but so is the blower . It is like the fan on switch on the thermostat is stuck but the thermostat clearly is still not doing anything. I did remove the ac low voltage wires but to no avail. The burner is not cycling on however. I am at a loss. It is almost like the furnace is trying to do 2 things at once???
  • Duckula
    Duckula Member Posts: 5
    Followup

    Removed all the low voltage wires from the t stat and re set the furnace breaker, the furnace tried to start as before. I am pretty sure now that the control board is bad ......not much else to check, or is there?
  • Henry
    Henry Member Posts: 988
    Control board

    I had a similar problem with my York. My wife called me at the office and complained that the AC was not working well. I got home early and found the house warm. The AC was working and so wal the burner! I disconnected the thermostat but it still kept firing. I had to close the gas valve to keep it from firing. I ordered a new board. It solved the problem!
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    The fact that

    your fan and combustion air blower are running says that a limit is open somewhere. Look for a flame roll out switch near the burners, the furnace high limit, spill switch on the draft hood or the auxiliary limit switch in the blower compartment. The control board is designed to bring the blowers on in the event one of the limits opens to protect the heat exchanger from thermal stress. It is actually called "self healing".
  • Empire_2
    Empire_2 Member Posts: 2,343
    Tim, My thoughts

    Exactly.  Many of the newer furnaces will give you a basic "lockout" which will bring on the blo and posibly comb. blower.  It's so hard to solve problems by what somebody say's, but We try  so hard..



    Peace



    Mike T.,  Back on the air..........................:-)
  • Duckula
    Duckula Member Posts: 5
    Problem solved

    I went ahead and called for service. The tech showed up and determined that the control board was bad. Voltage on one side, none on the other. Sounded reasonable to me, so he left after I said I could handle the job from there. I picked up a new board and changed it out.....re-set the breaker and same thing happened. I have since come to find out that my Honeywell Chronotherm III t-stat was displaying AC because it was not being powered from the control board ( AC Voltage) but rather it was running on battery power. I called the service tech and he came back to check the other voltages. Low and behold on the flame rollout switch on the right side of the burner box has a manual re-set on it. The switch was tripped ....once the manual re-set was pressed the furnace fired right up. No clue as to why the switch tripped but I am going to keep an eye on it. Thanks everyone for all your ideas. I got a bit of an education yesterday ....and a new control board. I had one go bad about 2 years ago so I am happy to have a spare. Especially when January rolls around.

    Jeff.
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    I do not think

    you needed a NEW BOARD as the problem was the tripped roll out switch, any limit switch opening on any forced warm air system will cause at minimum the system fan to come on and stay on and in some cases the combustion air blower also. You will also have an interruption of voltage so the furnace can't fire until the switch is replaced or reset. I hope you did not pay for a new board when you did not need one, also call backs should be for free.
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    There is also

    upon looking at the specs on this furnace the possibility of a combustion issue with the roll out switch being tripped and possibly the chance of Carbon Monoxide. Please get further checks done.
  • Duckula
    Duckula Member Posts: 5
    Final resolution to initial problem

    It seems as though this past week my furnace problem with the flame rollout switch resurfaced and as it turns out the senor was not bad, as a matter of fact it was working correctly .....Thank God. My heat exchanger was shot, as in corroded away on three of the tubes. According to the tech ( different HVAC Company ) than the last tech who merely hit the rollout re-set and got the unit to fire. The tech discovered the discolored sight glass, the melted wire coating and the fact that the unit has been overfiring with a supply gas manifold pressure of 5"wc.The unit was installed back when our house was built in 95 and had performed without a glitch since then or so I thought. The problem must have developed a few years ago and just became worse lately. Our weather has really been cold here in NEPA and the furnace has been running frequently to maintain 70 degrees in the house. I found the warranty card and it turns out that the heat exchanger was covered under warranty for 20 years .....lucky me. All I had to pay for was labor to change it out. I got away pretty cheaply considering how much a new exchanger could have cost me. I tempted fate by not having the unit serviced annually as the problem might have been discovered earlier. Sitting in an ice cold house last night was no fun at all .....don't neglect annual maintenance you might end up like me or worse. Should the flame rollout switch have not cut the burners out.......if the melted furnace didn't get my wife and I, I'm sure the C.O would have.



    Thanks you all the help.

    Jeff.
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