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"PID conflict" - smart pump vs smart boiler

I asked about a Viridian Delta T circ and its compatibility with a TT Excellence. Here is what I got:

"The challenge comes from the fact that both the boiler and the pump use a control loop to modulate, and the PID coefficients are not the same."

This is the same issue suggested to me by another wet head: that the PID control of the Prestige Excellence will be messed with by the Delta T pump.

Right now I have 3 speed Grundfos pumps but have been recommended by a contractor to consider the VT2218; Tacos new low flow pump replacing the Bumble Bee.


I wanted to upgrade from the split capacitor constant rate pump to an ECM and variable speed model. But not a Delta P for the same reason: possible conflict with my boiler's controls.

Taco tech folks assure me the Viridian will work on the secondary (circ controlled zones) and not interfere with the boiler working on the primary circuit.

Will the PID coordination cause a problem?


  • SWEI
    SWEI Member Posts: 7,356
    As long as you have proper hydraulic separation between the boiler pump and the system pump, you can run either a ΔP or a ΔT on the system side with no worries about the boiler's control coefficients.
  • Ken7878
    Ken7878 Member Posts: 4
    A PID loop works off of feedback from the process. If the process differs from the Set Point then the PID loop is going to react (its output will change) to bring the process back to the Set Point. If you have a second system altering parts of the system that the PID control system can't sense then it will not be able to control (maintain Set Point) the system any more.
  • Dave H_2
    Dave H_2 Member Posts: 526
    I have the same setup, I've got a TT for the space heating in my house and all of the circs are Delta T for the secondaries. The boiler circ is a fixed speed based upon the comments from the folks at TT and your concerns above. Let the boiler do its thing (boiler reset) and the circs do the load needs.

    Cant get any better. Actually it can, I also have modulating mixing valves (load reset) for the radiant floors and everything is working in harmony.

    Enjoy, Dave H
    Dave H
    Steve Thompson (Taco)