Announcement

Announcement Module
Collapse

How To Post Images

Want to know the how to upload images to your posts? Image Posting Tutorial
See more
See less

Direct vent wall furnace not heating up

Page Title Module
Move Remove Collapse
X
Conversation Detail Module
Collapse
  • Filter
  • Time
  • Show
Clear All
new posts

  • Direct vent wall furnace not heating up

    Hello all,

    Looks like the attached image. Tried to turn on the heater in anticipation of the coming winter, but it won't heat up. The pilot is lit and stays lit, but when I slide the thermostat temperature setting up, it doesn't turn on.

    I've replaced the thermostat with a new one and still the same result. Only two wires go into the thermostat. I've inspected the 3 wires going into the furnace and they appear to be fairly secure.

    I've read posts about replacing the thermocouple, but not sure if I'm looking in the right direction. Also not sure if its safe to disconnect the wires going in to the furnace and reattach. Are these low/milli volt, or 110V?

    Any suggestions? Thanks!
    Attached Files

  • #2
    Re: Direct vent wall furnace not heating up

    The problem is not your thermocouple or a gas related problem(possible but very unlikely). You have an electrical problem that cannot be solved over the internet. You need to troubleshoot the system. The line voltage is almost always 120v and your control voltage is 24v. You can touch 24 volts without being shocked but if you're sweaty or wet you'll get zapped. It sounds like you don't have an electrical background so it's best to call a professional. Are you sure your safety gas switch is on? Whatever course you decide, let us know what the results were. Thanks.
    Buy cheap, buy twice.

    Comment


    • #3
      Re: Direct vent wall furnace not heating up

      You might try this just in case, but it's not a fix.

      1. Shut off power to furnace and be sure it is off.

      2. If there really are only 2 wires at your thermostat (heating only) try shorting them together for this test only.

      3. Turn on power to furnace and give it a few minutes.

      Do you have any heat now? If yes, there's something not right with your thermostat. If there is still no heat, please do yourself a big favor and shut off power to your furnace and call in a professional HVAC contractor.

      Question: When you say "The 3 wires going to the furnace" are these from the thermostat? You may have the wrong 2 of 3 connected.

      Comment


      • #4
        Re: Direct vent wall furnace not heating up

        I know this sounds obvious but...........be sure the knob on the gas valve is turned to "on" and not set to "pilot".

        Post up a pic of the inside of your unit or pass on the make and model.

        Comment


        • #5
          Re: Direct vent wall furnace not heating up

          from what the picture shows it is a millivolt system, you can't use just any thermostat (too much resistance) it has to be for a millivolt system. these systems are very picky about bad connections because they don't generate enough energy to overcome much resistance. check all wiring and limit switches and that you have the correct thermostat. if pilot light is dirty the powerpile may generate enough power to hold in pilot valve but not enough power to pull in the main valve. or the powerpile is bad and too weak to pull in the main valve.
          Last edited by BILLG; 10-18-2007, 05:21 PM. Reason: add info

          Comment


          • #6
            Re: Direct vent wall furnace not heating up

            Originally posted by BILLG View Post
            from what the picture shows it is a millivolt system
            Bill, this system operates strictly off control voltage or does it operate in conjuction with line voltage?
            Buy cheap, buy twice.

            Comment


            • #7
              Re: Direct vent wall furnace not heating up

              It'd be just like a gas fireplace. Line voltage would only be required if you are using a fan kit which is optional.

              Comment


              • #8
                Re: Direct vent wall furnace not heating up

                Going to side with gear junkie Call a pro! I know its a cop out answer...but cnaces are u will do more danage ie $$$$$ playing with it than u will haveing someone come out and fix it right......check the ovious...does the BLOWER fan come on when u slide the t-stat up? if so..then sounds like a gas flow problem...if not then could be several things. FYI dont know about your area...but down here even if u get it narrowed down too part X most supply houses will not sell u parts....just the way it is.....unless they see a company shirt and van they treat u like a roach on their lunch box.

                Think about it this way, you and your family are worth way more than a few bucks u might...big might...save fixing your gas furnace....Liveing in Florida we dont do much with furnaces...heat pumps and Electric heat...some gas furnaces here...sooo even thougt Im an hvac tech....once I get so far I know to call buddy with more experience to help me solve the problem.

                Comment


                • #9
                  Re: Direct vent wall furnace not heating up

                  Originally posted by gear junkie View Post
                  Bill, this system operates strictly off control voltage or does it operate in conjuction with line voltage?
                  they use a powerpile system to avoid the necessity of 110 power and a step down transformer normally used with an external thermostat. it's cheaper to make and install.

                  Comment


                  • #10
                    Re: Direct vent wall furnace not heating up

                    Thanks for all the suggestions folks. In the past couple of days I found out some more info.

                    It's a Perfection Schwank model PDW850-SEM-1. It's a millivolt system with a pilot generator, not a thermocouple. Perfection Schwank became Schwank Group, which sold its excess parts to Texas Infrared. Kent H over at Texas Infrared was very familiar with the model and gave me a few suggestions.

                    I attempted swapping the thermostat with a millivolt compatible model from OSH with no luck. I tried jumping the wires at the thermostat. I also tried jumping the wires I believe are connected to the thermostat (they run into the floor below the heater) with no results.

                    I tested the voltage at the pilot generator and it was around 200mV. Kent had mentioned it should be in the 250~300mV range to adequately open the valve. I replaced the old pilot generator with one from ACE ($30). Tested the voltage to be around 300mV. Tried the thermostat again with no luck.

                    His last suggestion was to replace the millivolt gas valve (~$100). I've also been reading some other posts that suggest the valve might be stuck and can't open. Some posts suggest banging on the valve with a hammer to jar it loose. Sounds like it might be time to call in the pros.

                    Any other suggestions? The contacts and wires are all pretty clean/no visible corrosion. Thanks. I've attached photos.
                    Attached Files

                    Comment


                    • #11
                      Re: Direct vent wall furnace not heating up

                      hummm sounds to me like it is broken.














                      ha but what do i know? not to much when it comes to that stuff anyways. by the way my post is just a joke and nothing more so do get all mad at me and stuff
                      9/11/01, never forget.

                      Comment


                      • #12
                        Re: Direct vent wall furnace not heating up

                        did you jump the gas valve to see if it fires (from the middle terminal to the outer one without the other powerpile wire)? doing this bypasses all other wiring-limits & stat. if it works it's not the valve.

                        Comment


                        • #13
                          Re: Direct vent wall furnace not heating up

                          Thanks everyone for all the great suggestions. After vacuuming vigoriously, banging on the valve to make sure it wasn't jammed, going down the pilot generator voltage testing and replacement route, and finally calling in a pro...

                          Turns out it was a loose wire after all. It was the one that goes from the center connection into the gas valve. For whatever reason, the wire was actually extended about 6 inches with a spade connection.... and that one was loose. I had disconnected the pilot generator and thermostat wires, but never considered the connection from all of that into the valve itself was severed.

                          Well $60 in labor for a 15 minute visit means I can return the $10 thermostat, the $30 pilot generator, but I'll keep the $15 multimeter I picked up. Dumb noob move not yanking gently on all the visible wires just to see, as least I'll know exactly what to look for the next time it stops working.

                          Comment


                          • #14
                            Re: Direct vent wall furnace not heating up

                            Thanks for sharing the fix with the rest of us. Professionals know to check all connections as you described but it's a learning process. I know the same advice can be applied to other electrical problems. One that comes to mind is Automotive. Always make sure the connection is not only tight but that there is no dirt or corrosion causing a problem, even slight voltage drops can add up to significant problems.

                            Comment


                            • #15
                              Re: Direct vent wall furnace not heating up

                              Cool glad it worked out DoASfan......as for lose connections...happens...yesterday I was doing an install at a condo...condensor on the roof.....fire up the unit...airhandler runs...condensor does nothing....light up a smoke ..must be on a 5 min delay....5 min later check the wire nuts...yep had a little 24volt wire lose...duh Happens to the best of us.

                              Comment

                              Working...
                              X