I'm like the previous post...I don't know what you mean by flange. But, if it's the water heater relief valve and it is open (popped) that would explain why you have virtually no water pressure. I would be guessing that the water level dropped low enough in the water heater to stop flowing out of the water heater but is still not allowing pressurization of system. Are you running on city or from fresh water tank?
Mike & Cindy, (of course with Lucy the Miniature Schnauzer & Eddie the Yorkie) Dublin, VA / Fun Finder TT / X215WSK