Review on Highly Efficient 110V NPT3/4'' Domestic Water Circulation Pump With 3-Speeds For Hot Water Recirculation And Solar Heater/Faucet Applications (RS15/6G) by Shaylon Bateson

My positive rating is for the stainless version I ended up using (RS15-6SB). I had initially purchased a non-stainless version of the same pump under a different "brand" (KolerFlo) and the issues I had are summarized below but I'm 99% sure the issues with that one would also apply to this BokyWox line so I'm including my review for people to hopefully learn from.TLDR: The non-stainless version WILL rust; try different versions (and different "brands") of this pump if yours doesn't seem to pump enough water; ensure your pump comes with the pipe fitting adapters (that have o-rings) because the threads are NOT true NPT-fit threads and will leak; instructions are a joke so read enough reviews/do your own research to make sure you know how to install this (it's not complicated but the instructions make you question your own intelligence); no "on/off" switch so plan to use with a switched outlet or smart outlet for control.This review is for a non-stainless KolerFlo unit I bought (RS15-6 Blue). I intended to use it with the Grundfos-made thermal bypass valve for creating a water recirculation circuit for my tankless water heater system. I saw several reviews that said this worked for people, but it was not always clear whether they had a tankless system or not. Tankless water heaters require a minimum amount of water flow to turn on (typically 0.5gpm) and after plumbing this pump and the bypass valve, I discovered that I would only get about 0.3gpm through my water heater. I tried all the power settings on the pump, "bleeding" the air with the screw on the front and flushing the lines, nothing helped. "Bleeding" with the air screw did let out some spits of air/water but the way the o-ring seal is designed, there is no way to get it to seal again while the pump is running so beware of doing that and/or be prepared to get wet. I "knew" that the fittings were 3/4" MIP so I also bought all the associated hardware to plumb this into the existing copper hardline on the INLET to my heater (used SharkBite fittings + 3/4" coupling to a 3/4" nipple so that I could have something rigid to use for mounting with 3/4" pipe clamps). The installation was fine except that even with a more-than-typical amount of teflon tape, I was not able to get a leak-free connection between the coupling and the pump. I made the connections quite tight and I was worried I would over-tighten and crack something. I did make a simple plywood base to allow the flat sections of the pump to rest since my pipe situation would not support the pump on its own.Since the pump did turn on and wasn't overheating or making any weird noises (it was very quiet actually), I assumed that I was just out of luck since the Grundfos valve kit I purchased actually did explicitly state that it was not for use with tankless water heaters (though it said the reason was that it was not designed to be used with systems that had a water-return circuit). After a couple of days I uninstalled the pump again to see if I could figure out if there was something mechanically wrong, and that is when I saw the RUST in the pump. I was very disappointed to see that and also very upset that I potentially put my family at risk for having that in our drinking water system. I also read someone else's review about making their own parallel valve circuit with two Grundfos valves and additional hoses/fittings to allow twice the flow through the valves. So in a second round of attempting to get functioning water circulation, I bought all the pieces needed for making the parallel valve setup AND a stainless-steel version of this pump, but under a different name brand (BokyWok).Once I received the new parts, I first decided to just install the new pump and see if that would make any difference. I was surprised to find that there was actually an adapter in the kit that would connect to the pump with a 3/4" female O-RING fitting and then adapted to a true 3/4" NPT thread. I didn't end up using them, though, because I just tried to connect the SharkBite adapter hoses directly (the non-SharkBite end had a 3/4" female o-ring connector) and used some thick cardboard spacers to allow a standard 3/4" pipe clamp to secure the whole thing in place to my plywood base. After this simplified installation was done, I turned on the pump and the heater kicked on! This was WITHOUT making any changes to the Grundfos thermal valve installation, and I was now seeing about 0.5-0.6gpm flow through the water heater.This has been installed for a couple of weeks and still working fine.returning the crappy pump I received and the now unnecessary additional thermal bypass valve components. Lots of small lessons here, but my biggest suggestion is to try at least a couple of pumps from multiple vendors if yours isn't working. I looked at many pumps and they all seem to be the exact same imported hardware with various branded stickers on them (including the "official" Grundfos ones).