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return water temp control
I have 2 year old Crown CT-3 with a Riello 40 F5 oil gun. I am zoned with circ pumps, 3 fin tube baseboard zones and an indirect fired domestic water heater. A Taco SR 504 Exp controls the beast.I want to add a low temp zone (a small radiant floor zone) and a corn/wood pellet boiler to the mix. Presently I have a problem with low return water temp that is causing condensation on the inside of the boiler. I need to incorporate a system bypass of sorts, manual balancing valves won't work because of the variable loads with different rt's. that leaves electronic mixing controllers, mechanical mixing valves 3or 4 port. If I use a 4 port valve and boiler reaches temp, valve will be fully open and circ pumps will be pumping in series- not good. I have already resigned to the fact I have to build a new boiler board, but I want it to be the last one. Who has used what with success? Ideally I could snap an expansion board in the 504 mount the supply and return temp sensors and let it drive a 3 port mixing valve on the return line. I have not been able to find such offered from Taco without running on outdoor reset which doesn't work well with FT in upstate New York. Any advice would be appreciated!