Is the connection a plastic fitting? If so, and the water laying in the hose is hot, might explain it. Threads may be messed up. When you say "city tap" are you running a hose from your house? Does the hose have factory metal ends? What happens in a campground with the city water connection?
Lot of questions I know, but we need more to go on.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT