After reading several posts about issues with recirculating systems and balance valves, I feel that everyone has hit on all but one issue which seems to be my problem.

My shower will start out with hot water but slowly get considerably cooler after a few minutes. This is a new house and never had the problem until about 2 months ago - progressive got worse. I am not running out of hot water as I have plenty of very hot water at all faucets in the house. My system is plumbed with a check valve in the cold water supply line and also with a check valve on the exit of the recirculating pump in the dedicated return line. There is a surge tank in the common cold water feed line after both check valves. I believe that the check valve in the cold water supply must be leaking. I do feel the line before the check valve getting hot when no hot water is being used.

After many evaluations and twice changing the balance cartridge, I found a test that likely confirms the leaking check valve. Since the pump and heat increases the pressure on the hot side, if the valve is leaking (slowly)and no water is being used, the pressure on the hot and cold side will equalize. So, when turning the shower on and setting the temperature, the pressure is equal on the hot and cold side of the shower valve. As the hot water is used, the pressure on the cold side valve (cartridge) drops because the cold water pressure is less than the hot side pressure. The response by the balance valve is to reduce the flow rate of the hot (or increase the flow of the cold). Because the temperature was selected while the cold and hot pressures were near equal, the response of the change in pressure causes the shower temp to cool down.

To further analyze the problem, I decided to run the hot water tap on the sink that is adjacent to the shower, and leave it on when using the shower. Walla - hot water and it stays hot at (or very near) the initial setting. It does not continue to cool down. So, my theory is that the check valve leak causes the hot and cold pressure on the balance vale to be equal. But if the pressure is allowed to stabilize at the differential pressures created by the pump, and the temperature is selected while the pressure is imbalanced but stable, the shower valve/cartridge works fine.

I would appreciate any thoughts or comments on this before I change out the cold water supply check valve.



Edited 1 times.

if it were a check valve problem then all faucets would be affected.

since you are DIY and labor cost is not an issue:

change out the check and see what happens

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