Sounds like a relay on the power PCB is sticking in the on position and the shower is continuing to heat the water even after the power is switched off.

If this is the case them you will have to replace the PCB

It may be a faulty element in the heating tank (there are two, three in 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.

Could be 2 or 3 things.

Is the light on at the pull cord ?

No light could mean a faulty pull cord.

If the light is OK then next you need to check the solenoid, see below.

It may be your solenoid valve, you can check it if you have a multi meter, you should have a reading of at least k3.5 ohms, across the two terminals any less and you need a new valve. (Check the valve in the failed state.) (When it is not working!)

If there is power getting to the solenoid and it is not operating then there is a good chance that you have a faulty solenoid.

If you don’t have a multimeter we sell them 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 and letting you know much power you have left in batteries

(So you will know if they are good or not) and lots of other jobs, in short they are well worth a few pounds

http://www.showerdoc.com/installation/electrical-products/SKYTRO-600-005-Digital-Multi-Tester

If the solenoid is OK then Check the TCO, see below.

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 all these are OK then you probably need a new power PCB.

First What size is your fuse? It needs to be 45amp.

If the fuse is OK 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.

http://www.showerdoc.com/installation/electrical-products/SKYTRO-600-005-Digital-Multi-Tester

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.

http://www.showerdoc.com/installation/electrical-products/SKYTRO-600-005-Digital-Multi-Tester

The other thing to check is the outlet TCO

The outlet Thermal Cut Out this is a black disk with two wires going to it and it is mounted on the out let pipe (The bit between the heating tank and the hose)

Examine the connections closely if you see any discoloration / signs of overheating then the TCO needs replaced.

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 it is heating at all the TCO is OK

There are two other possibilities 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.

http://www.showerdoc.com/installation/electrical-products/SKYTRO-600-005-Digital-Multi-Tester

Or a faulty outlet TCO

The outlet Thermal Cut Out this is a black disk with two wires going to it and it is mounted on the out let pipe (The bit between the heating tank and the hose)

Examine the connections closely if you see any discoloration / signs of overheating then the TCO needs replaced.