A: 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.
If these valves are not fully open then there may not be enough water
getting to your shower to cool it properly the overheat safety device will turn
the power off until it cools Then it all starts again
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
If the shower is completely cold and there is no heat at any time then you may have a faulty Thermal Cut Out
A faulty TCO will have no continuity across the two terminals (The black thing on top of the heating tank)
Therefore a good TCO will have power at both connections and a faulty TCO will have power at only one.
(The function of the TCO is, if the water over heats it cuts the power off to the elements)
See Video.
http://www.youtube.com/user/showerdoc#p/u/2/_zi8JbEMYMs
Answered 22 days ago | The Doc