Read some related questions here but none of them seemed to address my exact problem:

Bought a house this year that has the water heater in a closet near all the bathrooms. The only long run goes to the kitchen sink/dishwasher, where it will take 2+ minutes to get hot water, much to the wife's annoyance.

Investigated and found a circulation pump (Grundfos up 15-42f) in the crawlspace with a setup very similar to the picture below.

I'll skip the stories of the pump being clogged, burning out, dealing with home warranty, etc but go right to my questions:

  1. What improvements can we make to the system? Right now the pump is either continuously on or off, only controlled by a switch annoyingly located in the crawlspace. My hopeful improvements would be:

    • Move the switch into the closet with the water heater (luckily the pump and switch are located right under where the heater is).
    • Add a timer so that it turns off at night (wife works from home so uses hot water throughout the day)
    • Add isolation valves before and after the pump so that I can isolate it for repairs, etc.
    • Get a pump that has either a demand sensor or a temp sensor, or both.
  2. When the pump is off (such as at night or right now when it's broken), will the cold water supply feed back through the pump (ignoring the shown arrows)? I expect it does because when I went to drain the water heater and closed the cold valve right on the heater, water would still go into it - feeding from the cold street supply all the way backwards through the hot line (I think). I had to shut off water to the whole house at the street to get it drained.

    • Would this partly explain why it takes so long for the kitchen to get hot water? It's pulling water both from the water heater and from the cold supply?
    • Would this cause problems for the pump?
    • Should we install another check valve between the pump and the cold supply line?

Thanks for the help.

Water Heater Setup

4 Answers 4


To awnser your first question I would advise checking your local plumbing and electrical code before relocating the switch as it may be required to be within sight of the pump (this is so a service tech can easily see that the powers is off and no one has turned it on when they weren't looking) Instead you could add another switch in series and locate that beside the heater.

Isolation valves are always a good idea (as you said for future service work)

Instead of getting a pump with a thermostat built into it you could buy a clip-on aquastat and mount that on the copper piping in the kitchen and run a cable back to the pump as it may be cheaper. And then there will be no need for a timer.

For your second question there should (hopefully) already be a check valve after the pump but before the tee fitting enter image description here

This is to prevent the cold water going back through the pump (one this will make your hot water cold as you said and two it can spin the impeller backwards and damage the motor). If there is one it might be worn down and have failed in which case you will need to replace it. If there isn't one then you might want to add one.

  • Good idea about checking the code. Will do. I believe the kitchen pipes are PEX (red tube?). Do clip-on aquastats work on those too?
    – Log
    Jan 3, 2018 at 22:10
  • No an aquastat will not work on pex but there should be a short copper or braided steel line from the faucet which ties in to the pex lines. The aquastat should work on that (copper for sure braided steel not sure) Jan 3, 2018 at 22:36

2) not all circulation pumps come standard with a check valve. Laing pumps for example have two different manifolds. One with and embedded ball check valve and two without ( thread or sweat) for 1/2” copper. Turns out I’ve opperated my system now for almost 6 years without a check valve and only really started noticing backflip issues when my pump started to go and cold water from the supply line was pushing past my pump and into the hot water system. It’s more apparent in the hot water systems closest to the recirculation line and not so bad farther down stream.

  • Hello, and welcome to Home Improvement. Good answer; keep 'em coming! Jan 19, 2019 at 15:18

Grundfos makes a pump that has a timer built in. Set it to come on about 1 hour before the water is likely to be used. Definitely make sure there is a check valve between the cold water valve and where the pump ties in to it so hot water doesn’t bleed in to your cold water. Last thing to check is if the recirculation line goes to the kitchen and then back to the pump. If it does then it’s plumbed correctly. If not then put a tee in the line going to your kitchen sink hot water and run it back to the pump. Good luck. Hope it works out or has already worked out.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here. Aug 15, 2019 at 0:20

1: I would put an "occupancy sensor" type switch in the kitchen that ran the pump when motion was detected in the kitchen. For an improved solution, it would pass through a thermostatic switch (sensor on kitchen faucet line) that would not let it turn on if already hot, and switch it off as soon as hot. I'd also insulate the hot water lines quite a bit, if not already done.

2: There's supposed to be a check valve in the pump.

check valve

If it works correctly and has not been removed, it should not backflow. You can get a replacement parts kit for it. You could also add a separate external check (in which case you should remove the pump's internal check.)

  • 1. Huh, I didn't know that "occupancy sensors" existed. Are they just a wall-mount motion sensor? Agree about the thermostatic switch. 2. I couldn't find any reference to an internal check valve in the documentation I found (pexuniverse.com/grundfos-up15-42f-circulator-pump)? They are replacing the pump so I'll make sure the new one has one internal.
    – Log
    Jan 3, 2018 at 21:20
  • For example: supplyhouse.com/… Yes, an "occupancy sensor" is basically a motion activated "light switch" but in this case you would not be using it for a light.
    – Ecnerwal
    Jan 4, 2018 at 2:34

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