I have a manabloc system. Actually, there are two Manablocs (it's a big house). There are no leaks, and I do not experience any slowness in receiving hot water at any sink. My problem is the opposite- when I turn on cold water to sinks, within a fairly short time pretty warm to hot water comes out and lasts for probably 10-15 seconds before returning to cold. This is more an annoyance than anything else except that hot water comes in similarly on the cold water line for the washers. I have tried to find anyone with a similar issue on the internet but have not. What could be the problem with the installation?

? how hot ?

? summers temperatures and lack of insulation ?

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Thank you for your kind response. The two-story house is very well insulated. All piping is inside of the outer walls and also is not in the attic (i.e. no pex is in the outer walls or attic, just interior walls) and the "hot when supposed to be cold" effect is year-round. It does not fluctuate noticeably from winter to summer. On temperature, when you switch on the cold, roughly 5-10 seconds later it can turn fairly hot, enough that you want to take your hands out from under the faucet to wait for it to cool, which can take 10-20 seconds or maybe more. Perhaps I should time it exactly.

I wonder if there is heat transfer from the proximity of the hot and cold pex lines- perhaps they end up being next to one another at some point during the run. From the basement I can see that hot and cold line bundles that go up into the house are sometimes clipped together at various points (or up inside the walls run beside one another, for all I know).

Alternatively, I have wondered if there is something wrong at the core- the manabloc units. I have two sets of 28 and 8 units by Vanguard. There is a top part with 14 on each side, the ones on one side being hot and the other side being cold, and attached below to it another small one with 4 on each side, in each case being all cold. Would this be a usual installation?



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I would look for a recirculating line that may be leaking hot into cold somehow.

This sounds like what happened after I put on of those recirc pumps on my water heater to get water to the kit faster..the crossover under the sink makes the cold warm about 10-15 seconds.then it cold...best money I ever spent...



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Plumber Dan, if I understand your post correctly, you set up the recirculating pump to get hot water to your sink faster and the byproduct of this is that the cold water line also gets hot for 10-15 seconds after you turn it on as well? This was a tradeoff you were willing to have.

Do you have a timed re-circ and a tankless water heater?

Have to check on the first but no tankless water heaters- have two gas-fired tank water heaters