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  • My turn for a question

    Cant believe I am asking a service related question, but this pos Lennox has me stumped.

    First a little background: A friend of mine just bought an abandoned house next to his bar. I was there a few weeks ago and fired the furnace for the first time in about a year. I couldnt get any pilot gas and I discovered the orifice was plugged. I redrilled the orifice and the thing lit off on the first try and had been running fine until Friday.

    This is a 80% Lennox. I cant remember the date code but I think its a late 80's, early 90's. Its the pos that has the motorized combustion air door. This is a spark-to-pilot with a Johnson Controls G77 ignition module.

    I get there Friday and find the ignition module in lockout. I reset the power and the thing goes through its normal start-up routine. Combustion air door opens and closes its switch. Within 5 seconds I get spark, pilot gas, and pilot ignition. Within 1 second of having a lit pilot, the pilot drops out and the ignition module goes into lockout. It does this every time. If I turn the control knob on the gas valve to "off", the ignitor will continue to spark until it reaches its time limit. But with the gas on, within 1 second of the flame sensor sensing pilot flame, the module kills power to PV.

    I had a used module with me which I tried and that had no effect. It doesnt help matters that I have been busier than hell, its colder than a witches tit in this house, and this is a freebie call.

    The only thing I can think of is maybe the flame sensor is generating too much current beyond the upper threshhold of what the module is set for. I've never ran into that scenario before, but its all I got.

  • #2
    Re: My turn for a question

    Originally posted by Ruudacguy View Post
    Cant believe I am asking a service related question, but this pos Lennox has me stumped.

    First a little background: A friend of mine just bought an abandoned house next to his bar. I was there a few weeks ago and fired the furnace for the first time in about a year. I couldnt get any pilot gas and I discovered the orifice was plugged. I redrilled the orifice and the thing lit off on the first try and had been running fine until Friday.

    This is a 80% Lennox. I cant remember the date code but I think its a late 80's, early 90's. Its the pos that has the motorized combustion air door. This is a spark-to-pilot with a Johnson Controls G77 ignition module.

    I get there Friday and find the ignition module in lockout. I reset the power and the thing goes through its normal start-up routine. Combustion air door opens and closes its switch. Within 5 seconds I get spark, pilot gas, and pilot ignition. Within 1 second of having a lit pilot, the pilot drops out and the ignition module goes into lockout. It does this every time. If I turn the control knob on the gas valve to "off", the ignitor will continue to spark until it reaches its time limit. But with the gas on, within 1 second of the flame sensor sensing pilot flame, the module kills power to PV.

    I had a used module with me which I tried and that had no effect. It doesnt help matters that I have been busier than hell, its colder than a witches tit in this house, and this is a freebie call.

    The only thing I can think of is maybe the flame sensor is generating too much current beyond the upper threshhold of what the module is set for. I've never ran into that scenario before, but its all I got.

    Ruud,

    Can you narrow down which POS Lennox model for me...there are so many to choose from

    I never liked the Johnson G77 control module. It doesn't reset so when it goes into lockout...no heat. Finicky little bugger that was subject to grounding issues. I assume the used one you installed was from a working system and gave you the same results?

    Ive never seen a flame sensor knock out a module before either. You may be over thinking this.

    With the gas knob in 'off' position try to trick the module by heating the sensor with a torch and see if it locks out when it sends voltage to gas valve. My guess is if the sensor is ok then the short is likely in the gas valve.

    If you can't figure it out, go back to the bar next door and have another drink, then try again

    Comment


    • #3
      Re: My turn for a question

      Originally posted by plumberscrack View Post
      Ruud,

      Can you narrow down which POS Lennox model for me...there are so many to choose from

      I never liked the Johnson G77 control module. It doesn't reset so when it goes into lockout...no heat. Finicky little bugger that was subject to grounding issues. I assume the used one you installed was from a working system and gave you the same results?

      Ive never seen a flame sensor knock out a module before either. You may be over thinking this.

      With the gas knob in 'off' position try to trick the module by heating the sensor with a torch and see if it locks out when it sends voltage to gas valve. My guess is if the sensor is ok then the short is likely in the gas valve.

      If you can't figure it out, go back to the bar next door and have another drink, then try again
      Does this unit have a thermocouple or thermopile to detect flame? If not, heating the flame sensor probebly won't work. I believe a small current of electricity is actually transmited through the flame sensor and flame and back to the control. sounds like a bad flame sensor. Try sanding it off carefully or replacing it, also check that the wire from the flame sensor to the control has continuity or it's not grounded out.

      That what goes on with power vent water heaters. Furnaces may be different. If I'm wrong The bar is still an option

      Comment


      • #4
        Re: My turn for a question

        saysflushable
        You are correct! A flame will let electricity pass through it where raw gas won't. The flame sensor isn't majic either, it's just a piece of metal to complete the circuit.
        Clean or replace the flame sensor!
        Good luck, and stop at the bar for a drink anyway
        Mike
        Last edited by myakka; 01-27-2008, 08:59 PM.

        Comment


        • #5
          Re: My turn for a question

          saysflushable and myakka: This isnt the classic symptoms of a flame sensor failure. I clean and/or replace at least 10 flame sensors per single heating season. Normally there is atleast a 5 second window in whatever type ignition module is used for the flame sensor to prove pilot flame (on spark to pilot systems) or main flame on direct ignition systems. I'm being generous when I say the pilot stays lit for a full second. Its probably closer to a half second. I did clean the flame sensor a few weeks ago when I had the pilot assembly out.

          Comment


          • #6
            Re: My turn for a question

            Originally posted by plumberscrack View Post
            Ruud,

            Can you narrow down which POS Lennox model for me...there are so many to choose from
            Yeah, its a G something.

            Originally posted by plumberscrack
            I never liked the Johnson G77 control module. It doesn't reset so when it goes into lockout...no heat. Finicky little bugger that was subject to grounding issues. I assume the used one you installed was from a working system and gave you the same results?
            Actually I have no idea where this other module came from. It was in a Honeywell S8610U1003 box. But, since they are both doing the exact same thing, I kinda ruled out the box being bad.

            Originally posted by plumberscrack
            With the gas knob in 'off' position try to trick the module by heating the sensor with a torch and see if it locks out when it sends voltage to gas valve. My guess is if the sensor is ok then the short is likely in the gas valve.
            You might be onto something there. I might even take it 1 step further and unplug the wires from the gas valve too. This is just the kind of problem that could give me fits. Sometimes it sucks not being a 'parts changer'.

            Originally posted by plumberscrack
            If you can't figure it out, go back to the bar next door and have another drink, then try again
            Been doing that alot lately. The g/f is about ready to kick me out of my own house.

            Comment


            • #7
              Re: My turn for a question

              pull the wire for the main valve and then cycle it and see if the pilot stays lit. if it does it may be a shorted gas valve (rare) or other wiring problem on main valve side (more likely). my thought is that control senses flame and tries to bring in main valve and loses power from either short or high resistance. check voltage while under load to control if pilot does not stay lit. check micro switch on damper door.

              lennox whisper heat

              Comment


              • #8
                Re: My turn for a question

                flame can prove in .8 seconds. I think BillG is on to it.

                Comment


                • #9
                  Ding ding ding.

                  Originally posted by BILLG View Post
                  pull the wire for the main valve and then cycle it and see if the pilot stays lit. if it does it may be a shorted gas valve (rare) or other wiring problem on main valve side (more likely). my thought is that control senses flame and tries to bring in main valve and loses power from either short or high resistance. check voltage while under load to control if pilot does not stay lit. check micro switch on damper door.

                  lennox whisper heat
                  He's right; it's a Whisper heat, (G20)
                  My first thought would have been to swap out the Johnson control for the S86, but you're right, it's unlikely that you have two bad controls.
                  I would also look at the door switch and the gas valve.
                  Also related to the gas valve: The gas valve has an orange wire that goes from the PV terminal (if memory serves) to the "Valve Sense" terminal on the BCC3 (or BCC2) board. If you've got a short knocking the control out, it may be here. This wire needs to be hooked up as it is what starts the timer for the fan to come on.

                  Comment


                  • #10
                    Re: My turn for a question

                    Thanks for all the responses guys. Yes, this is a G20 Whisper Heat. I wish I had a more definitive resolution of what exactly happened, but someone had been messing around with this furnace this weekend. When I got there this morning the SSU was turned on and the motorized damper door was open. Nothing else was happening so obviously the ignition module was in lockout. I tried resetting the power and nothing would happen other than the damper door opening.

                    I swapped the original G77 for my used replacement and it was only giving me intermittent spark. Just what I need, another completely different set of circumstances to try and diagnose a problem from. Atleast this time though, the problem appeared to be ignition box related.

                    So I wired up the closest Honeywell replacement which now is a S8610U3009 and the thing fired off 5 times in a row.

                    I'm pretty critical of myself and try to figure out all of my mistakes. This time though, I'm not sure what I did wrong. Other than trying an ignition box which I wasnt completely sure about.

                    I'm not a Lennox dealer and I usually turn down Lennox service calls because of all the proprietary parts that I dont have access to.

                    The good news is I have loads of free beer to drink at the bar now!

                    Comment


                    • #11
                      Re: My turn for a question

                      And just when you are absolutely positive it's the gas valve that needs to be replaced.....check your incoming gas pressure. If it's out of range (too high or too low) will cause lockout as well.

                      I only mention this because last year I worked in an abandoned house that the gas company had plugged the meter after nonpayment. Well they didn't plug it completely. The plug passed just enough gas to keep the pilot lit but when main burner fired....click...click...click......lockout Drove me nuts for over an hour. Kicked myself for not checking pressure earlier.

                      Whatever you do find wrong be sure to post it up here so others can learn from it

                      Comment


                      • #12
                        Re: My turn for a question

                        Good thread, hopefully others will read and remember what they read when they get out in the field.

                        We replaced a 50 gallon gas water heater after the previous one had about 10 years on it and the pilot kept going out.

                        We then sold the homeowner a new one, A.O. Smith, and the same thing kept happening, the pilot kept going out. We left the doors open to get more air in the room and checked the draft too.

                        It turned out being a bad regulator outside the house, just passed BGE (Baltimore Gas & Electric) responsibility.
                        Proud To Be Union!!

                        Comment

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