Truma frost control valve explained. How to drain down the water system open all water taps in the van if they are mixes have them in the central position fully open if you have a BMC conversion you will find your drain down valve next to your truma heater right hand side this is how to drain the system please watch the video and as always leave your mixer taps open all the way through the cold weather. This will avoid any damage to the taps pipework and your heater. BMC CONVERSION @everone #tru