Dennis, put in an F&T trap on the outlet of the heater. No check valve, no vent. That should make it work fine with a condensate tank. BTW, I happen to have a Hoffman tank and pump that had about 4 years of use. It was removed when I put in the new boiler and went to a gravity return. It works great. It's a Hoffman WC-6-20B. It has a cast iron tank. I'd take $400 obo.