The valves are powered with the key on and pass water unless the control ground is applied. In the "clicked" blue position the control ground should be steady. In the "clicked" max red position the control ground is removed and water flows. All other positions have the valve being pulsed with a pulsed ground signal. The pulses are large unless right at the switching temp.

Thus, unlike most heater water control valves, this valve actually control the amount of flow of water (or heat). Most valves are just open or closed.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician