Where is the solenoid coil in my electric shower?
From what I can see all your power is going to the heater with just a safety switch to keep it from getting two hot no solenoid I think one of the 2 things on the right side is a pressure/ flow switch but it has been several years since I worked on my unit, I have a similar unit in my barn and if I try to get the water two warm it barely runs this is the limitation of these small 30 amp units. I adjust the flow to my unit in the winter because the water delivered to the unit is colder and to keep the water warm enough to bathe horses I have to reduce the flow and mixing percentages. In short you may not have a solenoid controlling the water but just a pressure/ flow switch to turn the power on to the small heat tank when there is demand. The stabilizer in your model is more of a tempature regulator not a solenoid , measure the water temp output is it aproxametly at the set point? If so it is working correctly these units do have a limited heating range.