I talked to a guy who has a rheem tankless water heater. It quit on him and the plumber told him it was the gas valve. He now has the valve and wants to sell it for $500. Is this something I should steer clear of? He said he went without hot water for a week then caved and got a rental. Now just wants this one gone. Also he said it needs a venting kit so also curios on the price of that if any one knows. Thanks for now.