Hot water recirc problem

[Cjlambert]

We have installed the plumbing for a massive addition onto an existing house. Pictured below is the schematic for the entire house’s water distribution system.

All of the new shower valves we installed have their partition stops closed, the check valve and pump are definitely in the correct orientation, and at no point does a hot feed tie into a cold feed (obviously...), except downstream of the check valve (where the recirc ties back into the cold feeding the water heater).

With the recirc pump turned on, and all valves in the schematic open, there is no problem.

However, with the pump turned off, and the ball valve next to the pump closed, and every valve on the addition’s hot manifold closed, 5-10 minutes later, the old/existing hot feed begins to drastically drop in temperature, to the point of hardly any warmth at all. Also noticed that the recirc main on both sides of the check valve become Very cold, (even 15 feet upstream of the check valve).

Why is this happening?

 

[James Henry]

I wanna know how you had the patience to draw all those dotted lines.

 

[Sponsor]

 

[James Henry]

It's the mixing valve.

 

[Cjlambert]

Replaced the mixing valve already, it did not solve the problem.

 

[James Henry]

replacing it has nothing to do with it. the valve might be allowing cold water enter the hot water line depending on the adjustment. that's what its for.
set it to all the way hot and test your pipes again.

 

[Cjlambert]

It’s maxed out hot

 

[James Henry]

the line between the check valve and the tank is cold because it is connected to the cold water line. if you had a valve between the mixing valve and the existing hot water line you could isolate the mixing valve and rule it out as a cross connection.