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Issue: Hot water slow (90-120 secs) to come to distant fixtures Recirc system: 2 dedicated returns, merged to single pipe, feeding a 103258LF Bell & Gossett (NBF-9U/LW Pump 1/40 HP Motor) pump installed at the “Space Heating Return” inlet (where drain valve is) on our 50gal Bradford White water heater. House: built in 2014, 3600sf, 2-story, 10 foot ceilings, upstairs bathrooms on opposite sides of the house, water heater on ground floor roughly centered. Kitchen about 25 feet from water heater. 2nd story bathrooms roughly 20-30 feet horizontally, & 12-15 feet vertically removed from water heater.

Pump seems to be oriented correctly (arrow pointing down toward the water heater) and it gets quite hot when it runs. It seems to be running normally, gently vibrating and very quiet. This system has never worked—no change in time to hot water whether pump is running or not. I don’t know where the 2 return lines come from—upstairs & kitchen (or maybe both upstairs)?

Is this pump sized right for our home? What else could be wrong?

Recirc Pump, return lines

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  • Are the pipes coming out of the wall hot before the pump turns on? How quickly does the pump get hot? How long does it take for the pipes coming out of the wall to get hot after the pump starts?
    – longneck
    Commented Nov 7, 2019 at 19:32
  • Looking at the time clock it is almost always running or almost not running , I usually set recirculating systems to turn on every 15 minutes around time of use and then only every 30-60 minutes during unscheduled times. I would make sure the timer is working or check if it has a heat sensor those are the best, but if the sensor fails they don’t cycle properly.
    – Ed Beal
    Commented Nov 7, 2019 at 23:10
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    The pump impeller may have broken; the pump runs but does not pump water. sounds odd but that is what happened to my sons' pump. Commented Apr 28, 2022 at 15:18

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When the pump is running the pump and piping around the pump will get hot even if there is no water flow. Check the spring loaded check valve, that brass thing between the pump and the water heater to make sure that it's arrow is pointing down also. more possible problems; 1) The pump may not have enough "head" to push water through that spring loaded check. If that is the case, remove it and replace it with a standard swing check in the horizontal piping above the pump. 2) The pump may be air bound and will require that a vent valve be installed in the horizontal piping above the pump to purge the air. That type pump will not push any trapped air in the pipe. The air stays trapped and the pump will not pump. The installation looks OK except for the spring loaded check and the pipe above the pump not having a vent valve. I have the same pump on my hot water recirculating lines that handles 3 bathrooms and it works great. I set my timer to run the pump 15 minutes each hour and for 2 hours in the morning and evening when we normally take showers. my 2 cents

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It appears that the pump was installed without unions on both ends. The bottom connections appear to be threaded and the top return pipes are soldered. The vertical installation requires special low melting point solder and the body to be wrapped with a wet rag and not to over solder. The installer may have damaged the impeller during installation when soldering. The other cause of failure as noted by @d.george is the system has to be completed vented of air at the highest point. This is the instructions from the installation guide, "Do not start pump until the system has been filled and vented. Air should be vented from the system by means of an air vent located at a high point in the system. The system must be completely vented prior to pump operation." –

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  • I believe you are looking at the unions as the top and bottom connections. The spec sheet for the -9U model lists the connections as "union."
    – aghast
    Commented Aug 31, 2021 at 14:57
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    There are unions on both ends in plain sight.
    – Ecnerwal
    Commented Dec 29, 2021 at 15:20

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