How is my hot water recirculating system installed?

... and why is it not working like it should?

Moved into a house recently that was built in 2006. There is a hot water recirculating pump installed (Grundfos UP 15-10 pump). I'm not very knowledgeable about plumbing from a DIY perspective, so I could use some help here.

I'm having some problems with it now, as it's no longer providing hot water as quickly as it used to. I looked up the service manual for it, and it calls for an installation different than what I'm actually seeing (not sure if this is the problem, but I want to understand). The manual specifies:

  • it should be installed at the hot water discharge from the tank in the direction of the flow
  • a thermal bypass valve should be installed at a sink furthest from the tank.

What I actually see (Or think I see):

  • There seems to be some sort of dedicated return line coming out of my wall
  • The pump is there with the flow direction pumping back into the tank
  • It pumps back into the release valve of the tank
  • There is no "thermal bypass valve" anywhere in my house

So how does it actually work and how can I fix it? What's the easy stuff to check?

Here are some pictures:

Oh yeah baby the water heater

Close up of the pumping system

Close up of the pump

  • 3
    Couple quick comments: the green valve is the drain for the tank, not a pressure release. The thermal/pressure release is on top (probably that white pipe going into the wall). And I'm personally disturbed by the electrical outlet in the same part of the wall as plumbing. I've personally always made sure a stud is separating electrical from anything else, not sure if there's a code for that.
    – BMitch
    Commented May 28, 2011 at 22:42
  • 2
    Great observation on the electrical outlet directly below the PVC tubing. Couldn't find a direct reference in NEC quickly. But sure looks like a disaster waiting to happen!!!! The obvious code infraction is that a GFIC is required within 8 feet of any water supply. The receptacle in the pic is not a GFIC. Commented May 29, 2011 at 11:16
  • Also looks like a pipe is leaking where it returns into the tank
    – Steven
    Commented Nov 11, 2012 at 0:23

7 Answers 7


You're sorta kinda in a bit of trouble here. This system is close to being good, but because of a seemingly minor screw-up, you're going to have major problems here. The recirculating pump SHOULD NOT be connected to the drain.

First off, it's quite possible that the segment of pipe between the pump and the "tee" attached to the drain valve is completely or partially clogged with (corrosive) scale/sediment buildup. Judging by the scale buildup on the outside of the pipe just below the tee, it looks like the tee is leaking (why? corrosion?). I can only imagine that the inside is worse. Even the check valve and the ball valve upstream from the pump look like crap. In fact, I'm pretty sure that's calcium on the ground below the check valve (thing between the pump and the drain with a hex bolt -shaped top on it), indicating that it too is already leaking. The check valve almost certainly isn't functioning properly (check valves are intended to only allow water to flow one way,) which is possibly why you are having to constantly readjust the temperature in your shower. The cold water gets injected into the tank at the bottom (via a long "dip tube" that enters at the top and travels down to the bottom.) If this check valve is being held open by sediment, or if it has failed due to corrosion, then cold water could be coming out of the water heater from the drain at the bottom, making your "hot" water turn merely "warm" after about 10-15 gallons of use, which is one possible explanation for your "shower get[ting] colder during use" problem.

My advice would be to get this junk removed ASAP before something bursts and you have a disaster on your hands. Get rid of it completely, or if you want to get it fixed up, get a new pump (Grundfos makes great pumps, but I can't imagine that this pump is usable at this point) and tell the plumber to connect the recirculating pump to the T&P relief valve inlet, which is not currently being used(?), rather than the drain. Doing this would reduce the scale/sediment buildup greatly, which happens mostly near the bottom of the tank. Replace all of the pipe in the vicinity of the pump as well, as it is probably completely scaled up and corroded. Everything else should be ok.

I see a line (the CPVC that goes into the wall) for what I hope to be a T&P valve, but I can't see where the actual T&P valve is. If it's tee'd off of the hot water outlet, then that's fine. I'd hope it's not simply laying on top, not connected to anything, but I don't have enough faith in whoever installed this to take that for granted.

  • Do not connect the pump to the T&P valve! That's not safe. Connect it to the cold water inlet. The port above the Energy Star label is not a T&P valve inlet. A.O. Smith heaters sometimes have extra ports specifically for recirculation, but I don't see one at the bottom - the top one would be the output.
    – Ariel
    Commented Feb 3, 2023 at 9:32

What the manual is describing is a system without a dedicated return line. The valve at the furthest point allows previously hot water that is now cool to go into the cold water pipes backwards and the pump pushes hot water back into the hot pipes up to that valve. With an existing install, this is probably the easiest way to do it, but I prefer an install with a dedicated return to avoid getting the water from the hot water tank in the cold lines (not a fan of the mineral taste). It looks like you have the latter setup.

The first thing I'd check if you're having problems is when the timer is set. You typically want this to run shortly before you get up in the morning to use the sink/shower. Over time, with a power outage now and then, it may be running after you need the hot water.

  • I've had the timer disabled and the pump running constantly and the problem persists.
    – snicker
    Commented May 28, 2011 at 23:04
  • 1
    Next guesses would be that either the pump is failing or that the pipes have a blockage. I'd start by finding the other end of that return line, if possible, and make sure there isn't a valve closed there.
    – BMitch
    Commented May 29, 2011 at 0:44
  • Your first paragraph was spot-on. The real problem appears to be that it was improperly installed. I would suspect from someone who is new to using return lines. Commented Oct 28, 2011 at 5:24

Very interesting problem you have here. Both Mitch and Michael are right and cover the potential problems. I'm gonna add a third observation. I personally would NEVER allow heated water to infiltrate the cold water supply. The water coming from most water heaters is filthy, dirty and full of bacteria.(especially if temp is set below 140F) The sediment in the bottom of most heaters is nasty! I always advise my customers to never use hot water for potable purposes unless it is going to be boiled in the process. With that said, the closed systems I have had installed cycle the unused hot water back into the cold water supply to the heater tank with a back flow preventer installed in the cold feed to prevent the warm water from entering the cold supply by siphoning. The system as pictured looks to me like a quasi sediment agitating system, by pumping water in from the bottom of the tank. NASTY!!!! There is a reason for a drain at the bottom; to get rid of sediment as well as drain the tank to replace it. I would rethink this system, get some advice from a Master Plumber that knows how to install a recycling system if you feel you need it. Most residential users do not need instant hot water, have the high volume usage or have hot water outlets located so far from the heater to justify the additional operating costs of this type of system. Don't get me wrong, loop systems are great if the lines are well insulated, and the volume of hot water required can justify the cost.


Actually the return loop line coming back to the tank should have the pump at that point. After the pump the return line should run back to the cold supply line to the top of the take with a tee and shut off valve on both legs of the tee. One leg should go to the cold supply in with a check valve on the cold supply side to prevent the hot water from backflowing into the cold supply. The other side of the tee should go to the hot supply line to feed the house with a check valve to prevent backflow. the shut off valves on each leg should be close 1/2 to divert roughly equal flow to the tank and the hot supply. This configuration will give you true circulation of the hot loop as intended.


This device recirculates the water in those hot water lines by placing a sensor and a valve at the farthest end of your hot water line that senses when the water in the hot water line has dropped below 95° F, opens the valve and “trickles” the water out of the hot water line into the cold water line until the water in the hot water pipes gets back up to 95° F or so.

  • 1
    There is no valve, it is not needed with a dedicated return line. Commented Oct 28, 2011 at 5:27

My perfect advice would be to return the feed immediately back to the top of the tank on the cold side, check valve included. This way continuous circulation happens inside the tank rather than taking chances with a whole house system. You might also install an extra pump at the top of the loop to help balance out the bottom pump, etc. A third pump in between is optional although highly recommended. The idea here is to get the water spinning fast enough to cause friction ergo the generation of heat.

  • One more thing...
    – heather
    Commented Jun 25, 2014 at 21:11
  • If I remember my Three Stooges Plumbing and Electrical Course correctly, the temperature pressure relief valve exit tubing (PVC) pictured directly above the 20 amp wall outlet qualifies.
    – heather
    Commented Jun 25, 2014 at 21:19
  • Just thought of gluing a cork inside the PVC terminal end. Problem with electrical safety solved...
    – heather
    Commented Jun 25, 2014 at 21:21
  • 1
    Instead of commenting on your own answers, edit them, that way you can make a cleaner looking response. Commented Jun 26, 2014 at 12:58

check valve is looking a little crusty. they dont hold up well in potable water. cold water from the bottom of the tank will "back" through the pump amd mix with the hot giving you the diminished hot water that you descriped.

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