3/4" Bypass Valve

Have my house set up on a domestic hot water recirculation system and run that through my hydronic bath towel warmer. The towel warmer has a thermostat on it so when the thermostat turns off, the Taco by pass valve allows the recirculating system to still work.

Need parts for gas boiler. It fit well

Taco really fumbled the 3/4" NPT union outlet on this part. It doesn't mate with any stock fittings. Typically you'd use NPT pipe threads with tape to create a water tight seal. However, since this is a union, you need to use the flat face of the housing to create a seal. There are exactly zero parts that have a 3/4" male screw thread with a flat face to mate to this part. If you screw a 3/4" male adapter or a nipple, there's a enormous 1/8" gap between the fitting and the mating surface (because it's a union, simply screwing the threads tight will not create a seal). As NPT threads are tapered, you're never going to overcome the gap by turning before you destroy the nut. I hope that Taco wasn't trying to create a ground joint union as this would be obnoxious with a $50+ part and impossible given the tapered threads. You could try to mate the male end of a 1/2" union to this part (which nominally fits and may have been the original intention), but unions have tapered or scalloped mating faces, not flat mating faces. There would be no seal. Again, no solution. So I'm going to try to fit a 1/8" thick washer between the mating surface and a 3/4" male adapter. That's a really unstaisfying solution to what should have been a properly designed part.