11 inch emersion heaters are crap and don't last long a simple test for anyone is just a lightbulb lamp holder and a piece of 2 core flex take cover off power it up and put one lead on the neutral on element and other on the live going in to thermostat if it lights up there's power there then transfer lead on to output from thermostat to element if it lights up the element in heater is knacked. if it doesn't light its the thermostat faulty
How old is the cylinder? Is it foam covered or just copper?
I'm guessing you have never done this before, these jobs have a habit of going wrong very quickly
Nice one. Don't forget to use heat resistant cable.
If you're replacing the heating element you'll need to just break the tension on the threads of the element before you drain the tank. Doing this ensures that the pressure of the water in the tank stops the tank sides distorting under the initial torque required to undo the heating element. Once you've got it started leave it hand tight so that it doesn't leak, then drain the tank, and then it's a relatively simple matter to replace the element once the water level is low enough. Working in reverse, synch the new element up by hand before filling the tank and then tighten fully with your wrench once the tank is sufficiently full.
If you're replacing the heating element you'll need to just break the tension on the threads of the element before you drain the tank. Doing this ensures that the pressure of the water in the tank stops the tank sides distorting under the initial torque required to undo the heating element. Once you've got it started leave it hand tight so that it doesn't leak, then drain the tank, and then it's a relatively simple matter to replace the element once the water level is low enough. Working in reverse, synch the new element up by hand before filling the tank and then tighten fully with your wrench once the tank is sufficiently full.