Digital Thermostate dosen't Work with 356 mixing Control

Ram_3

I cant get a honywell T8400B Digital T stat To controll the Tekmar 356 mixing controll. I plug the T stat in, and the 356 Calls for mixing demand with the t Stat in the off position. The 356 serve's only one mixed Zone. I have the T stat wired derectly to the 356 conrol red to T White to Com., the 356 Is powerd by the 24 volt power source from a taco SR504 EXP zone pump swithching relay controll box. Im able to get Old School Mercury T stat to work fine. What's Up with this.

Frank_17

tstat

you need an isolation relay,simple cube relay will work, isolate the 24 volts

Jay_12

Power stealing tstat

This is a known issue. Power stealing thermostats require current to power the thermostat even when the thermostat is not calling for heat. The 356 registers this "trickle current" as a mix demand.

This can be corrected by either connecting an isolation relay to isolate the 356 from the thermostat or it has been found in some cases that a 1000 ohm resistor in parallel to the "T" and the "Com" terminals will also correct this.

If you have any questions, please call tekmar tech support.

Jay www.tekmarcontrols.com 250-545-7749

S Ebels

The 8400

These stats came with the required resistor if I recall. It should be in the box. If that doesn't do it, you'll have to do the isolation relay thing.