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Wiring Grundfos single zone relay and pump to Rinnai E50C boiler

eddo Member Posts: 12
Finally found the time to finish the boiler installation, and I'm having a brain freeze. I have some of the wiring done, but the installation instructions that comes with the relay (and to a lesser extent, the boiler) leave a lot to be desired for an amateur. It's a single-zone system with one thermostat. So, here's a list of questions (be gentle!):
- I'm running the 120v power for the pump (and by extension, the relay) and the boiler through one switch so everything gets shut off together for repair, maintenance, or emergency. Usual practice?
- I'm fine on how to power the pump through the relay, and to connect the 2 wire thermostat wire to the relay. But I'm less clear on connecting the relay/pump to the boiler. From the illustrations (attached to this post) it appears the boiler has a separate 120v line in for power, and the relay connects to the boiler (24v TT wiring?). If so, then where on the attached boiler illustration does the wire attach, the thermostat connector?
- I'm also a bit fuzzy on the Rinnai illustration of the external pump connector (green block, 2nd from left in illustration). Maybe I'm so far off-base and the relay actually goes to that Rinnai connector (and therefore is 120V). And to make me even more confused is the note for that green external pump connector warning about not connecting a pump directly because of a call for heat or DHW energizing that circuit.
- Any help? Thanks!


  • Ironman
    Ironman Member Posts: 7,119
    You don't need the pump relay. Simply wire the pump directly to the green terminal marked "external pump". Then wire your thermostat to the black terminals marked "room thermostat".

    If you need the common wire for the thermostat, temporarily put a jumper between 22 & 23 thermostat terminals and measure between there and the pink 24v terminals separately. The one that gives you a 24v reading is the common; the other should show 0v between it and 22 & 23.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Ironman
    Ironman Member Posts: 7,119
    If you wanna use the relay, connect the upper "no & c" terminals to "22 & 23" on the boiler.

    Make sure you install the outdoor sensor so the boiler can operate from its reset curve.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 3,611
    edited November 2018
    Like Ironman says, you DO need the pump relay because it says that E series models will energize the pump on a call for heat or DHW. You don't want that pump to run on a DHW call because it will fight with DHW production and you won't get enough hot water.

    Keep the pump relay and wire it exactly as shown on your diagram.

    "NO" and "C" on the upper right of the pump relay drawing get wired to #22 and 23 on the boiler. They tell the boiler to fire.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hourTwo btu/ per sq ft for degree difference for a slab
  • eddo
    eddo Member Posts: 12
    Thanks guys. Yeah, that system pump 120v connector block on the boiler was confusing me. It still does. If you shouldn't connect a pump directly to it why is it even there? Maybe Rinnai uses the same electrical panel on their Q models too, and the system pump connection is used for that, but not my E model.