Troubled by RV Doc Response

I have trouble with your answer about the check valve on water heaters you addressed in an earlier question. I am sorry, but I have never seen one on the cold water line. The only ones I have seen have been in the hot outlet on the tank. Norman, (Milford, NH)

Norman, you'll find a backflow preventer oftentimes at the cold water inlet, right at the back of the water heater. It's preferred by many of the better manufacturers in order to prevent hot water from migrating back out through the cold inlet. Here's why; If a branch cold line is tee'd into the fresh water system right at the water heater, it could siphon hot water out of the heater and into the cold system. I've seen a few RVs with the water heater located in the lavatory, under a cabinet and in close proximity to the toilet. The customer would get hot water (and steam!) rising from the toilet if he flushed the toilet with hot water in the heater. They thought the cold line to the toilet was plumbed incorrectly but by adding a check valve at the cold inlet, it rectified the "steam in the toilet" issue.

Not all RV manufacturers install a backflow preventer or check valve in the cold inlet because of the added cost and the fact it is not a code requirement, but some do as an added benefit to the end-user. It's a good thing, so let not your heart be troubled any longer!