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Adding an Indirect to a combi boiler
So we replaced the old oil burner and boiler with a new gas unit, a Bosch Greenstar 150k BTU with tankless hot water rated at 4 gpm continuous. Contractor said would have as much hot water as ever needed. I am having a problem with temp fluctuation that nobody can figure out. Both of the upstairs baths have been recently repiped and with new fixtures and both behave the same way....water is cold at first then warms up and gets hot as you would expect (HW temp is set at 140*). Then about 2-3 mins later it gets noticeably colder to lukewarm, then goes ice cold for about a minute then back to hot. I don't know if the cycle repeats since we don't take unusually long showers.
I have searched for an answer and come up empty so I am considering adding a zone and going to an indirect HW heater. Had a 40-gal Buderus in our previous home and it was amazing. Can I just connect the output from the combi HW coil to the indirect tank and then add a heating loop for the circulator? Almost sounds too easy....