A: If there is no water then it is probably a faulty solenoid, if there is some water then the solenoid is probably OK.
If there is some wate rthen the things to check first are.
1 That the main valve coming into your house is fully open.
2 Then check that the valve on the line to the shower is fully open.
Make sure that the shower head is clean and clear, that the hose isn’t kinked (this can happen just behind the hand set where it is difficult to see) also check the inside of the hose although it can look OK on the outside it could have collapsed internally
The other possibility is a faulty flow/stabilizer valve not allowing the correct amount of water into the shower.
A ruff check is to remove the shower head turn temperature control to fully hot the water coming out of the hose should be a bit more than a dribble then turn to fully cold and it should be coming out at full flow.
If there is not much difference between the two then you could have a faulty flow valve.
Answered 198 days ago | The doc