Desired street water pressure to Navien CH-210ASME-NG

What is the desired street water pressure to the auto feed valve for the navien ch-210. Should the contractor have install a pressure regulator and backflow preventer before auto feed valve? Tanks-a-lot for any input.

They generally should work fine with anything that is considered 'normal' for a domestic water system. Typically, the upper end is 80psi...more than that, and you should have a PRV to keep it at or below that. Most houses work fine with something above 40psi or so. Auto fill valves should have a backflow preventer on it to prevent boiler water from getting back into the potable system.

What is the minimum desired street water pressure.

Having less than 30psi can be problematic, but still functional. People live with gravity feeds with less. Some things don't work well much less than 30psi though. At 20psi, some things will stop working, like some toilet fill valves. A typical boiler usually has about 14-15psi internally, and needs to be pressurized at least up to that point. If the street pressure is low, but you have good volume, you can add a pump to raise it to whatever you want.

I am asking specifically for the minimum pressure to the auto feed valve of the boiler. The contractor installed a pressure regulator before the auto feed valve and would like to know if this is necessary and if so what pressure should it be set at as it pertains to the navien CH-210ASME-NG

Most autofeed valves are adjustable and are designed to operate at normal home pressures. If your street pressure exceeds 80psi, the whole house should have a PRV, not just the autofeed. As long as the autofeed can provide the desired boiler makeup water, it should work fine regardless of what's behind it. Whether it needs one there or not is another question.

The answer to the question, the autofeed valve for the navien need no less than 40psi to function correctly and no more than 140psi. I learned this the hard way. My contractor installed a pressure regulator before the autofeed valve with very dissapointing results. Once the pressure regulator was removed with street pressure to the autofeed valve, all is good.