Hot water heater

[Pedro]

Ok, after a weekend trip, this is what's happening, hot water from both sides for a few seconds, then both hot and cold are working normally although my dad was shocked how hot the hot side was,,, it has never made hot water from shore power, not sure if it's the element or t stat,?

[catalina_mike]

So I locate a 1/2" brass check valve from FWWebb, $8 , haven't even found the check valve on my system if there is one, water is now acting normally I wonder what happened?

It unstuck open..