For reading temp I’m still using the Fibaro FGK-101 with a ds18B20 glued to a section of copper pipe.
I’ve bought the parts to replace the sensor with the BrewPi one mentioned above, but I haven’t installed it yet.
One problem I’ve had with the Fibaro is that the batteries haven’t lasted well with the activity that the sensor is seeing, so along with installing the new sensor I’m going to hard wire the fibaro to usb power, also as mentioned somewhere above. I just have to find the time to do the project.
The fact is the recirculator works fine without the temp sensor. I just have the pump run timed in my piston to run for 30 seconds at no less than 15m intervals when there’s motion in the bath. It’s slightly less efficient I suppose since the pump runs regardless of the water temp, but its really not that bad. I have a fuel stream that tracks the pump runs and it runs between 12-18 times per day for 30 seconds. So lets say 9 minutes/24h for nearly instant hot water every time?
I use the 2 pistons above in the thread, plus I have another failsafe implemented as a smart ligthing app that turns the pump off if the “power allowance is exceeded” and its been running for 1m. My hope is this catches a condition where the pump is on and ST cloud goes down, since Smart Lighting, and my zwave switch both run locally, but I haven’t fully tested that either.
As far as flow issues with the pump on, I haven’t seen any. I haven’t noticed any pressure differences with the pump on or off.