Tankless gas fired W/H

lonzu

Hello, I have been going through the posts but could not find a specific post regarding my problem. I have this vaillant Tankless gas fired W/H, when I open the hot water tap for the first time, it starts up ok, and as the tank is only about only five feet above the W/H I switch on a small pump for pressure and it fires up quite good. The problem is when I try to light it again after it is switched off for shampooing and soaping. When the tap is opened it dos`nt fire up and after some seconds it lights up with a bang and off again with the pilot lamp too, sometimes it`s scary. I was wondering if it could be that the first time the hot tap is opened, warm water gets in the system because the pilot lamp warms the water in the W/H copper pipes while afterwards it does not fire because of the cold water that gets in the system. Can someone please confirm my suspicion and how to solve this problem. Sorry for writing so long

Thanks

beenthere

Have someone run water while your down watching the unit. And then see what it really does.