Hereby, share the three main roles of the different pressure bypass according to E-top OEM room thermostats in different system:   1st:  Protect the end control valve of the heating system to prevent the pressure difference between the two ends control valve from being too much. In normal heating system end control valve: one is floor heating’s manifold electric heating valve, the other one is thermostatic radiator valve (TRV). Both of their close pressure difference is about 10m, if the pressure difference too large, the valve can not close. But in daily use, if pressure difference is over 3m, means 30KPa, there will be noise in the control valve. So we just need to prevent the noise of the control valve, it will be easy to solve the problem of the close pressure difference.   2nd:  Protect the mainframe to prevent the mainframe flow from being too small. For air source heat pump (thermostat), if mainframe flow is too small, there will be a warm causing mainframe stop working. For boiler system (thermostat), if mainframe flow is too small, it will make boiler On/Off frequently, even overheat protection then turn off the boiler.   3rd:  Protect water pump (thermostat) to prevent pump head too large due to the small flow. For water pump in the system, including build-in and out pump, if flow is too small, it will cause the pump head too large. At this time, water pump will deviate significantly from the ideal working state point, increase energy consumption and motor overheat.   These three roles work when the system is under partial load, that is, when part of the end is closed. Depending on the system, sometimes three roles work at the same time, sometimes only one or two of them work(s).