A: The Fault
If the shower is absolutely cold then I think 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)
If there is some heat it may be a faulty element in the heating tank (there are two, three in most 10kw showers) you can check them with a multi meter you should have a reading of around 12>18 ohms.
If you have power to the elements and no heat it's probably the elements, no power to the elements then it's probably a micro switch.
If you don’t have a multimeter we sell them at £10 each with a guide on how to use them for checking and testing the various parts of your shower.
Apart from helping to fix your shower, they are really useful for checking you have a power supply to appliances, for checking fuses, letting you know much power you have left in batteries
(so you know if they are dud or not) and lots of other jobs, in short they are well worth the £10.
What may be the cause
I think you have a micro switch stuck in the on position when you switch off your shower one micro switch keeps the power on to one of the elements and perhaps boils off some of the water inside, then the over heat safety device comes in and shuts the shower down.
The next time you come to use the shower because the heating tank isn’t full of water it starts to boil and that is how the shower starts coughing spluttering and issuing steam.
This will cause the TCO or one of the elements to fail
So you will have to look and see if you can spot the faulty switch and then replace it.Answered 979 days ago | The Doc