Immersion heater size

Hi Mike, my daughter has just moved into a flat with a Pulsacoil 2000. I have found the reason she has little hot water is due to a faulty immersion heater thermostat, it is due to the thermostat pocket leaking. I need to replace the heater, can you tell me what length of heater I will need? I would rather have one ready to install rather than remove the faulty heater and then go to fetch one. I take it the draining down is fairly straight forward. Thanking you in advance.

Hi
Heater length is 11"
You can buy the proper one at
http://www.segel.co.uk/
Draining down can be slow sometimes.
As can filling, which is best done slow to avoid air locks
When the unit is full just switch the supply on and off a few times ( this starts the pump) And helps with any air.
DO NOT switch any heater on until you are sure the unit is full.

Thanks for that, very grateful.