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How does boiler mixing valve affect efficiency?
I have new a Laars Minitherm JV225NDISU2 natural gas forced hot water boiler with six zones of baseboard. There is a valve (picture) above the boiler which connects the system return water, just above the boiler pump, with the output of the boiler. I’ll call it a mixing valve. What is the proper position for this valve and how does position affect efficiency? How big is the effect on efficiency between half open and full open? Right now it is fully open.
Initially the valve was half closed and the boiler guy said that position was best for efficiency. But I had a problem where if one zone called for heat, all zones would get heat. The other zones would get heat even though their thermostats were set below room temperature. Opening the mixing valve now allows the zones to be independently controlled. Does this situation point to a different problem with the system?
I don’t get the theory behind connecting return to output and how that helps efficiency.