Hello everyone, this is my first post. I have installed a Navien NP-180 tankless water heater and am using it with my existing recirculator pump (Taco 006) and 40 gal. electric tank WH which has its breakers turned off. Water flows from the pump discharge, thru the Navien, then to the 40 gal. tank, then to the system, to return to the pump suction. The pump is controlled by a timer only - it has no aquatat. My water is very soft (less then 10 ppm) due to a water softener, and my recirc temp is only 105. The pump is controlled by a timer, on at 5 am off at 11 pm. The loop piping is CPVC or PEX and is fully insulated end to end. The 40 gal. tank is insulated with R-13 batt - not pretty but it is very will insulated.

I want to run this without an aquastat, but the Navien manual shows an aquastat in the tank to control the pump. A similar diagram on the Rinnai unit does not show, and apparently does not require an aquastat.

The system is piped correctly with check valves, exansion tanks, etc.

Everything seems to be working fine. I know it is not the most energy efficient, but there are only two of us, and our HW use is low.

Does anyone know if this system really does require an aquastat to cycle the pump?