Source: Beijing Viessmann Wall-Hung Boiler Repair http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3778856.
What are the characteristics of the Viessmann wall-hung boiler - steam overpressure interlock protection?
The signal for steam overpressure interlock protection usually comes from a pressure signaler with an electric contact control signal, such as an electric contact pressure gauge or a pressure controller. When the pressure exceeds the protection value, the electric contact operates and can output a control signal. There are two methods of its interlock control:
One is that when overpressure occurs, the wall-hung boiler automatically stops, and after the pressure returns to normal, it automatically ignites and runs again;
The second is the same as the low water level interlock protection, connecting the overpressure protection contact signal in series in the total control circuit of the low water level interlock protection, so that after the overpressure shutdown, even if the pressure returns to normal, it cannot automatically ignite and run again. Comparing these two methods, the former has two functions: pressure control and protection, while the latter only has one function: pressure protection. Due to the pressure control function, the former tends to operate frequently, making it less reliable than the latter; but the latter only has the pressure protection function, and its pressure control must be achieved by other means. Therefore, if both methods are used simultaneously, better results can be achieved.