problems with hot water recirculation

dmpaulApril 15, 2008

We just moved into our newly constructed house. The house was pre-plumbed for a hot water recirculation system. I installed a Grundfos 10-16 pump along with an indirect fired hot water heater. Problem is, the pump doesn't seem to do much at all, if anything. It takes several minutes at the second floor bathroom

I have a hose bib installed between the pump and the hot water tank. When I open it and let it run until all the water is hot, all the faucets in the house have hot water. So I assume the plumbing was done correctly.

I'm beginning to wonder if the pump is too small or there is some other installation problem. The pump is installed vertically, about a foot above the cold intake of the hot water tank, which is located at the bottom of the tank. The house is two stories, 1800 sq ft on the first, 1000 on the second, and the hot water tank is in the basement.

If anyone has any experience with these systems, I would sure appreciate any tips or things to avoid.

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The 10-16 is a very low flow. low head pump.

I am assuming that your water heater is an indirect water heater off a boiler and not a wall hung on-demand heater right?

If it is a on-demand, that pump will never activate the burner.

With regards to it being too small, a piping calc would be required to size the circ.

Size and distance of pipe going all the way out and back with a count and type of both fittings and valves. All that is needed to calculate the head.

FYI: during recirc and the system is closed, the run to the 2nd floor (height wise) has no effect as the water going up is compensated by the water coming down for most intensive purposes.

    Bookmark   April 15, 2008 at 9:42AM
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Yes, the water heater is an indirect fired heater. I plan on flushing the recirc line in the morning. I have a flow meter, so between that and timing how long it takes to get hot water, it should give me an idea of how big the loop is. It is 3/4" pipe, with a 1/2" return to the recirc pump.

How does one calculate the head? The water heater is about 5' tall, with the hot water leaving the top of the tank. The cold water inlet is at the bottom of the tank. The pump is about 18" above the cold inlet.

Another manufacturer of auto-recirc pumps (Laing) said in their installation manual that the pumping direction should always go up or level. I don't know if that's the case with the Grundfos (no mention of any such restrictions in their manual), but still I wonder if it has similar restrictions.

    Bookmark   April 15, 2008 at 3:14PM
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Head is the friction loss of total pipe plus calculations for all ftgs and valves.

The UP10 series was designed to be on the loop return, pumping down just as you have it. Any other way and the label, internal tstat (if you have that model) and clock would be upside down.

    Bookmark   April 15, 2008 at 4:09PM
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Good news! I have the system fixed. I disassembled the pump. Except for a few grains of sand, I didn't see anything wrong with the pump. Before reassembling, I plugged the unit in and verified the rotor was spinning. I put it all back together and re-installed it, and it worked perfectly.

I'm not sure why it didn't work in the first place; my best guess is the rotor was originally installed a little off center, or was bound up somehow.

Anyway, it now works. Thanks for the comments. BTW, it was pretty easy to take apart and put back together, so anyone with a similar pump should not be intimidated to attempt it themselves.

    Bookmark   April 16, 2008 at 12:38PM
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I had a recirculation pump with a timer for several years but it bugged me because most of the time the pump was running it was not needed *and* a lot of the times I wanted hot water, the pump was not running. I just finished installing a unique "on-demand" control that turns on the pump when I turn on the hot water anywhere in the house.

1) On the cold water IN on the Hot Water tank, I put a flow switch that turns on when it detects flow. (Note: This can *not* be anywhere in the circulation loop)

2) The flow switch turns on a Delay-Off timer that turns on the pump immediately, but does not turn it off for 80 seconds after the switch is turned off.

Now, when I turn on the hot water, the pump comes on and I get hot water fairly quickly. The neat thing is this: I can turn the hot water on for a second and then turn it back off...but the pump keeps going. I then just wait for a little bit and when I turn the Hot water back is hot and ready to use. However 80 seconds after I quit using the hot water, the pump turns off till the next time there is demand.

Parts I used:

Flow Switch: I used a Gems 26605 because I got it cheap on ebay. ( ) Others are available, but be sure to get one that has a fairly low trip point on the flow. (.75 Â 1 GPM)

Delay off Timer: I used an MX046 timer kit.
( I had to build it into a case, but it seems to be working well. There are other delay-off timers and relays out there but this seems to be the cheapest option. (Yes I am all about keeping the cost of my projects down)

    Bookmark   December 21, 2008 at 1:09PM
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I think I like this solution as much or better than using a motion detector - in combination with an aquastat - to control recirculating pumps.

With this solution, all of the wiring could be near the pump and wouldn't need to be run to the point of use. The only downside is the slight delay in getting hot water and knowing to briefly turn on the hot water to activate it.

    Bookmark   December 22, 2008 at 10:36AM
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If you didn't want to worry about using wires, you could just use wireless motion detectors. They're a little more up-front and require battery changes every few years, though.

Personally, I think there are members of my family who remain nameless that wouldn't remember to "prime" the hot water and would just let it run -- negating the pump.

Hence, we have motion detectors (wired).

    Bookmark   December 22, 2008 at 2:47PM
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Some of my family members don't seem to remember to prime the system either :-(. However, that does not completely negate the pump. Since the pump kicks on as soon as the HW is turned on, the water still heats up in about 1/4 to 1/3 the time it does without the pump.

I am considering adding motion detectors to some of the bathrooms (Particularly the guest bathroom). I would hook them in parrallel to the delay timer. However the kitchen/great-room in my house is where we spend most of our time...and a motion detector would keep the system hot nearly all the time... even when all we are doing is watching TV.

    Bookmark   December 28, 2008 at 12:36AM
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BTW: There is more detail on my installation over on a different thread:

Also, there is a diagram of my setup at:


    Bookmark   December 30, 2008 at 11:24AM
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Hmmm, the URL to the system diagram got garbled by the forum filter. Try this instead:


Here is a link that might be useful:

    Bookmark   December 31, 2008 at 11:21AM
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