Hot water heater recirculating pump

Discussion in 'Water Heater Forum, Tanks' started by Herb, Apr 4, 2021.

  1. Herb

    Herb New Member

    Apr 4, 2021
    Clovis, CA
    I have a Rheem heat pump water heater model number #PROUH50 T2 RU350 DCB with a Grundfos hot water recirculating pump model number #UPS15-55SFC/LC. The pump has been replaced 2 times already and it still doesn’t move any water. Attached is a connection diagram of the system. The flowmeter and thermocouples are used for energy monitoring on the whole house. The cold water supply has a check valve not shown in the diagram to prevent the recirculating return water from going back into the cold water line. When I turn on the pump the flowmeter will show a slight surge for a few seconds and then it quickly goes to zero. There is a hose bib on the discharge side of the pump and if I open it the flowmeter shows about 5.5 gpm flow. If I turn on the pump with the valve open it will increase the flow to a little over 6 gpm. And I then have hot water at the furthest faucet (kitchen) in the house inside of 20 seconds. Without running the pump or opening the valve it takes a little over 2 minutes to get hot water at the kitchen faucet. With running the pump for four minutes until the timer shuts it off it still takes two minutes to get hot water at the kitchen faucet. The flowmeter will show about 0.8 gpm with the kitchen faucet open full and if I then turn on the pump it will increase the flow to about 1.5 gpm. But without a faucet open the flowmeter indicates zero flow except for the momentary increase when starting the pump. My connection diagram seems to be too large of a file to attach to the post. But the pump is connected to the return side of the recirculation line and pushes the return water into the cold water inlet of the water heater. Hot water leaves the water heater and feeds the hot water recirculating loop in the house and then returns to the pump.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    With out a diagram showing how your system is installed, it's hard to tell what's going on.

    What are you using as your cross-over and where is it located - same with the pump, or, do you have a dedicated hot water return line? Check valves, depending on where they are could be preventing the water from circulating.

    FWIW, it's not a 'hot' water heater...if it was hot, why heat it?! It's a water heater that makes water hotter...
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  4. fitter30

    fitter30 Well-Known Member

    Feb 2, 2020
    Retired service tech
    Peace valley missouri
    Pump looks like its three speeds is it on high? Take some pics
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