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Mixing Demand on Tekmar 361

Hi there

I have a radiant floor heating system utilizing a Kitec manifold and a variable speed injection system that was built eight years ago to the Kitec specs.  The controller is a Tekmar 361.

A few days ago I came home to very warm floors.  I checked system and the supply water was hot; it's usually just lukewarm, even when the outside temp gets real cold.  The Tekmar indicated a mixing demand, which as far as I know should not happen when the room is already up to temp.  I checked all the settings and didn't see anything unusual.  I shut down the variable speed injection pump and let the water circulate through the floor zones overnight.  In the morning I turned on the injection pump and everything seemed to work fine . . . for about four days.  I came home today and the system is trying to pump hot water through the floor again.  The mixing demand indicator is on and the % indicator for the "Current output of variable speed injection pump" is maxed.

There <em>was</em> a power outage for a couple of hours the day before the floor was noticeably warmer.  But in the eight years of living here we've had tons of power outages with no ill effects.

I'm not a tech (obviously), but can anyone here tell me in relatively simple terms) what might be going on?  Or what I might be able to check?




  • Mark Eatherton
    Mark Eatherton Member Posts: 5,840
    Tough call...

    Could be a surge took out an internal co-processor and the logic is toast.

    Try powering it down for a while, then powering it back up and see what happens. Some times, when the unit is powering down, if it sees a surge, it upsets the eeproms on board, and they need to have their sinus's cleared out (power down and reset).

    Check all sensors to make sure you don't have a bad connect (thermally or wiring).


    There was an error rendering this rich post.

  • Yukoner
    Yukoner Member Posts: 6

    I should have thought of that.  That's what I do if my computer's giving me grief.

    Thanks, Mark.  I'll give it a try.

  • Randy Baerg
    Randy Baerg Member Posts: 26
    361 mixing demand

    You state that: "The Tekmar indicated a mixing demand, which as far as I know should not happen when the room is already up to temp."  For most applications the demand should drop out when no zones are calling, so this may be a mechanical issue.

    I am wondering what is providing the control with the mix demand. If you have zone valves with end switches or a pump relay end switch, then the end switches should open when the thermostat is satisifed and the control should shut down.

    Try turning all your thermostats down and check the 361 LCD to see if the Mix demand pointer turned off. If not then check your end switches. Is there a zone valve that is sticking open? 
  • Simply Rad
    Simply Rad Member Posts: 172
    Troublehooting 101

    I always try to look for the obvious or unobvious.  You also should check the heating demand signal, being your thermostats, zone controller and thermostat endswitchs.  Something maybe sending a signal for no good reason, or you could have a short in your control wires. 

    Jeffrey Campbell
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