So I piped an OWB into a guy's existing system yesterday. Boiler loop heats a 20 plate, Taco 007 draws hot water from the plate, through a mixer, into a Lennox Q90-100 LP boiler which serves an 8 loop radiant system. Now, I've done this dozens of times before and left the wiring up to someone smart, it works out fine but I've never seen a boiler like this Lennox that has no setpoint control. The only aquastat is a high limit, and when operating the boiler puts out 120 degree water and short cycles every 90 seconds or so. I turned the mixing valve up to 130 thinking it'd cut out the gas burner while the stat continued to spin the pump, which it did once the supply water had reached temp. Problem is though, that the inducer fan never shuts off. And every 5 minutes or so, the igniter would light up and gas valve open, fire the burner for 3 seconds and then shut down again.
Given the insulation quality and size of the loops, I want to run 100ish degree water through the mixer instead of 130. At that, the gas burner will want to run all the time. Dude wants to keep the Lennox in operation if possible as a backup and to keep the OWB loop from freezing up if need be, so adding another stat to power the pump only was all my feeble mind could produce. He wants to do the electrical himself, so I was wondering if any of you gentlemen could explain this to me so I have some insight on what to tell him. I'm at a loss. Thanks in advance