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Old 14-05-2013, 08:44   #16
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Re: Need help with plumbing re-design

That said, it's not worth my time to argue the point any further. You have seen what you have seen and I have seen what I have seen. We can go our separate ways believing what we believe.
It wasnt about an argument, I was looking for a technical reason, ( not a quote). Hot and cold water dont generally mix and in a pressurised system I cant even see how any serious leakage back to the cold, even if it did, so what!. In the installations Ive seen with no check , theres no bleed across.

heres a US manufactuer

again mixing and pressure relief. I mean a check valve would in effect be nullfied by the mixing circuit anyway. SO maybe its just an outdated practice

I always wondered why it was suggested


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Old 20-05-2013, 21:58   #17
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Re: Need help with plumbing re-design

Generally a check valve should NOT be installed on the cold water inlet to the water heater. Least wise without a thermo expansion tank. For the typical marine water heater with side hot and cold connects, thermosiphon is minimum.

But when heating water in the tank, the water does expand. Putting a check valve on the cold water inlet would prevent that and cause extra stress on the tank and downstream. The plumbing codes would not approve that without an expansion tank. Of course that does not apply to boats, but its still a very good idea.

On the diagram previously it showed a check valve after the accumulator. In reality the check valve should be BEFORE the accumulator. This as the accumulator will also act as a thermal expansion tank.

So generally there is no real reason to install a check valve on a water heater. 30 years ago it was common practice to install a check valve with a 1/8" hole drilled in the clapper at the inlet to the water heater. The hole was to allow relief of thermal expansion. That practice was changed 20 years ago.

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