Way back last spring when I was finishing up the boiler wiring, I had problems with the secondary pump such that I replaced the used pump I bought on ebay with a brand new Taco 011. That was expensive but not as expensive as buying more than one rebuild kit for it or guessing whether the capacitor was bad too. In the post about the pump problem, I promised to explain the change in wiring that the problems with the pump led me to, but I never posted about the wiring and now I can’t remember clearly why there was a problem!
I have some documentation that shows the changes in the wiring. This was the original pump wiring. The primary pump was wired to the boiler and the secondary was wired to the zone control pump end switch.
Original wiring diagram
This is a close up of the zone controller with just one pump wired.
Original Boiler Zone Control Wiring–the end switch is wired to the secondary pump
In this photo of the system, there are only two black wires to the boiler, one is the outdoor reset and the other is the zone valve thermostat end switch that tells the boiler there is a call for heat.
Original Pump Wiring
The secondary pump seemed to have issues with this wiring, it caused the secondary pump to run when the primary did not. That stressed the secondary pump.
I have a diagram of the wiring changes.
Zone Control with Mod-Con pump control. UPDATE: The secondary pump cannot be wired to the Priority Zone–instead both pumps are wired in series to the Space Heating Pump connection.
Close up of the wiring of the pumps on the zone controller.
Revised Zone Control Wiring-Both pumps on Zone Controller UPDATE: This wiring is an error and does not work–Priority zone even with the dip switch set to off, is always on with the NC connection and does not sync with the main boiler control with the NO connection.
Wires changed to boiler–if you can follow them. The boiler pump control wires are routed to the zone control end switch and the two pumps are both wired in series. This works!
Revised Boiler Wiring for Pumps
Although the changes made perfect sense at the time, I’m not sure why the Taco controller diagram for a Mod-Con boiler had the system pump on the zone end switch instead of from the boiler connection, or why the secondary pump runs without the boiler pump when not wired together. This is a problem because I want to add the third pump from storage and that would separate the wiring for these pumps again.