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tekmar 256 installation

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  • tekmar 256 installation

    Hi I am going to install a tekmar 256 unit on my gas baseboard boiler. have read the threads, but.............on my system, 24vac t-stat and 24vac zone valves, standing pilot light for the 24vac gas valve,w/thermocouple

    why not just remove one wire from the gas valve (comes from the honeywell aquastat) run it up to terminal 5 on the control panel and run another wire back to the gas valve.....tstat calls for heat, opens zone valve, turns circulator and the tekmar unit decides when to turn on the gas. keeps all other wiring intact..........but i must change the low limit setting on the aquastat to match what temp i set on the tekmar and also match the hi setting yea or nay????????

    since 5 and 6 are just blank relay terminals should work.?????????.

  • #2
    Re: tekmar 256 installation

    Without know what boiler and it's current wiring diagram I can't say for sure but I thought that the Tekmar control was not to recieve any power besides the 24 volt input
    Last edited by plumberscrack; 12-17-2008, 07:08 PM.


    • #3
      Re: tekmar 256 installation

      Just to throw my 2 cents in since you already helped me with this one plumberscrack. The 8 and 9 on the 256 need 24 volt power. 9 is common and 8 is the power side.

      5 and 6 are the control. based on the temp the from the sensors the 256 will decide wether or not to activate the relay inside it to close the contacts and allow current to flow (24volts only) from 5 to 6.

      ternminal 7 must be used to connect connect 7 to 9 only. How? I used the end switch on the zone valves to accomplish this. But there CANNOT be any power running there.

      So basically its, power to 8 and common to 9 comming off the 24 volt transformer. Than i ran a wire from 9 up to the switch inside the zone valve. than back out of the switch and to terminal 7. Once 7 and 9 are connected through the switch the tekmar now sees that there is a call for heat. Than based on the temp sensors it will determine wether or not to close the contacts that will connect 5 to 6. Which is the signall you will use to fire the boiler.

      Hope im not out of line posting on this. Just say the word and ......
      Slant fin S-120-DP boiler
      L8148E aquastat
      3 V8043E zone valves
      Tekmar 256 Boiler control


      • #4
        Re: tekmar 256 installation

        thanks for the reply, i appreciate it. looking at the schematic for the 256 it shows that the relay is just that, a single pole single throw 24volt actuated relay and it does nothing but transfer an imput to an output, terminal 6 to 7 or shows no internal voltage (other than to control the coil on the relay) the points are isolated

        i have not received my control yet, but i will put it on the bench and energize the relay and see if terminal 6/7 have 0 voltage. if no voltage is present then suppling 24vac to either terminal will work as the relay terminals are isolated from the tekmar control voltage.

        i will let you know thank you for your responce......


        • #5
          Re: tekmar 256 installation

          Hi received my unit today, wiring instructions state boiler relay (4/5) are DRY contacts and have a 5 amp capacity. so there is NO internal voltage applied to the contacts......and since the relay does not know what it is switching you may apply any signal or voltage as long as it is not over 5 amps....will let you know for sure when i bench test it........


          • #6
            Re: tekmar 256 installation

            Sounds like you are ok then if you have a standing pilot 2 wire gas valve on your boiler


            • #7
              Re: tekmar 256 installation

              Pulmmerscrack. thanks it's all ways nice to have "some one who knows" conform you theory.............

              Besides, now if the house burns down I can blame it on you!!

              JUST KIDDING<<<<<<<<<<<

              Merry Christmas TO All.........