Hot water recirc pump installed, now hot water in cold lines?

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hevykevy420

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Aug 23, 2010
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Austin, TX
Hi everyone,

I have a 1983 4,000 sq.ft. two story house with two 240V 50 gallon hot water heaters connected in series (not sure if thats the right term, but I believe the 1st floor HWH in the garage supplies hot water into the cold inlet of the upstairs HWH in the attic.)

For 5 years I wondered why it took > 5 minutes to get hot water to the kitchen sink. Sometimes the dishwasher water would not ever get hot. I discovered a capped off hot water return line in the attic at the 2nd story HWH (which supplies the kitchen) and an old recirc pump disconnected and thrown to the side with romex still attached. The previous owner replaced both HWHs but I guess cheaped out on the recirc pump :(

I installed/plumbed a taco 009 recirc pump on a timer and with an aquastat at the 2nd story HWH and now I have hot water fast in the kitchen which is great (and clean dishes).

My issue is that I now have hot water coming out of the cold side for faucets even on the 1st floor branch to the master bath and the upstairs showers are WAY too hot when the pump is scheduled. It is impossible to turn the temp on the showers down because hot water is coming out the cold side on the shower mixing valves. (I have both HWHs set at 120 degrees for upper and lower elements.)

The aquastat clipped to the return line is supposed to turn off the pump at 115 degrees, but it seems to run too long. (It is wired correctly and it does work, just seems to run too long on cycles.) I am guessing that because of the circulation pump, hot water is being "pushed" all the way back through the cold water inlet of the second story HWR and back through the 1st floor heater into the cold supply somehow?

What can I do to stop this? Can I install a 3/4" one way check valve at the cold inlet of the 2nd story heater to stop the mixing? Or is there another solution?

I have purchased a 4 gallon expansion tank but I'm not sure if i should install it in the attic at the 2nd story HWH or the garage at the 1st floor HWH. I'd rather have it in the garage incase it leaks ever, but maybe I should install in front of the proposed check valve in the upstairs attic to allow for expansion on the return loop. Any thoughts/advice on any of this would be greatly appreciated.
 

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