OK, just had to get a new tank for the Truma boiler, as reported in this thread. The previous one had pinhole leak. Problem was definitely not frost damage, but not sure what caused it. So now I want to be very careful with what I use to clean and disinfect the water system. Don't want to damage my nice new shiny (and expensive) tank. Truma say you should not used chlorine based cleaners. I used to use Puriclean powder whose active ingredient is Sodium Dichloroisocyanurate. Is that a type of chlorine? What do others use please for this cleaning please?