Cold water Inlet Checks on Noritz WH:

Why check it at all?

I've often questioned why it is that people put check valves on the cold water inlet to any water heater for potable water heating.



What's the reason? Code requires (here in CO) a vacuum breaker on the cold water inlet, but to the best of my knowledge, none of the codes require a check valve on the cold water inlet to any potable water heating system.



With you adding a storage tank to the mix, it will definitely change the expansion characteristics, which have to be accounted for in the way of a potable water expansion tank, but if it were a true tankless system, an expansion tank is a waste of time and money. The water is only being heated if there is a draw, which means its not a closed system.



In most cases where I see a check on the cold inlet to the tank, there is also a circulation return pump, and I think maybe the installing plumber is worried about the circulation return pump forcing hot water backwards into the cold water main, thereby ending up with hot water where only cold water should be.



Bunk.



In order to that to happen, there would have to be a cross connection that would allow the movement of water between the source and the point of distribution. I have NEVER installed a check on the cold water inlet (other than for controlling unwanted back flow in the C.R. line) and I have NEVER had ANY issues with unwanted flows.



I think it is one of those myths that got perpetuated but have never been proven. But as always, I try and keep an open mind, and am willing to look at it through someone else's eyes and field experience.



ME

Correct

Paul nailed it



When flow of cold is experienced resulting in pressure drop of cold side piping, water can back feed through tankless unit(s). Resulting in a nusiance fan operation at the least or a spike in hot water temps after pressure rises feeding back through tankless.