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What is involved in setting the drainback option (ODB) on my SmartMaxx-DHWPlus controller?

What is involved in setting the drainback option (ODB) on my SmartMaxx-DHWPlus controller?

In the submenu, switch ODB from “OFF” to “ON.” Four new items will appear in the submenu: tDTO, tFill, tSTB, and OBST. Some experimentation may be necessary to get these settings correct for your system.

  • tDTO (time period switch-on) is the amount of time the DT O must be met before the controller will turn the pump on. The factory setting is 60 seconds. The collector/tank temperature differential must be met for 60 seconds straight before the controller will trigger the pump.
  • tFill (filling time) is the amount of time the pump runs at 100% to push the heat transfer fluid up and over the top of the system piping. The factory setting is 5 minutes.
  • tSTB (stabilization time) is the amount of time the controller will ignore the DT F after it changes over to minimum pump speed. The factory setting is 2 minutes. This time is set aside because running the pump at 100% may cool the collectors below the “off” temperature differential. So, instead of shutting the system down as soon as it comes on, tSTB allows a time period for the collectors to stabilize at the minimum pump speed.
  • OBST (booster option) can be turned on if you have a second pump plumbed in series with the first. The second pump will then only come on during the filling time (tFill).

Turning on ODB will also automatically trigger the following changes:

  • The EM setting will be set to a fixed value of 200°F.
  • DT O will be set to a fixed value of 20°F.
  • DT F will be set to a fixed value of 8°F.
  • DT S will be set to a fixed value of 30°F.

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