There are usually three valves, although some kits do it with fewer. Basically, you put a valve on the cold incoming line, another on the hot outgoing line, and then run a line between the two (as a bypass), with a third valve. In normal operation, the cold and hot valves are open, and the bypass line valve is closed. When winterizing, you reverse it - close the cold and hot valves, and open the bypass. This allows the RV antifreeze to flow past the water heater so you don't have to buy 6 gallons to fill it. I use the bypass when I'm blowing out the lines in our trailer to save some headache (I don't use the RV antifreeze).marko wrote:I also can't find my white plastic drain cap -instead I have a metal pipe - which seems to just leak any water i put into the tank -
How do I fit a hot water cut off valve? IN the back under the closet? - is it just a matter of putting shut off valves on each of the water pipes going to my tank?
However, it's not as easy to install as you might be thinking: The issue is that the B190s were built with polybutelene pipe, and it was pulled off the market years ago after a bunch of homes had major leaks followed by a major class-action lawsuit (which resulted in homes, but not campers, all being replumbed with something else). So, to get room to install the bypass, you'll have to cut the polybutelene, then use Sharkbite fittings to connect to Pex or another kind of pipe. This introduces a bunch more connections in the system; i.e., new points of failure. It wouldn't be that hard to entirely re-plumb a B190, but that might be more work than you're willing to tackle at the moment.
I have one of the bypass kits sitting at home that I bought for my B190 but never installed after I realized the issue above. I think it's this one, which only uses one on-off valve, along with a check valve, to function - not exactly as I described above, but the concept is the same, just a little less valve-turning. If you have to pull the water heater, I'd definitely try to install one, and perhaps replacing the plumbing back to the next fixtures in the lines if possible (trying to minimize those extra connections).