Noisy Immersion

I have an Elson Coral E thermal store with 2 immersions - one is a booster which I never use and the other is the main controlled by a timer. The booster immersion sits in the middle of the tank, the main sits under it near the bottom. After 3 years the booster immersion has just had to be replaced due to a leak. Had to drain the tank which was a nightmare! When I now heat water using the main immersion the noise is incredibly loud. The plumber I called back now says the leak damaged the thermostat housed in the main immersion and plans to fit another after the weekend. However will this solve the noise problem? I've read other posts suggesting air in the tank, kettling and thermostat problems could cause the noise. According to the system literature the builders left me there are 2 thermostats - a control thermostat and an overheat limit thermostat - should both be replaced? Any advice would be most appreciated.

Did he fit the correct immersion or just one off the shelf. They normally cost about £50 from Elson to buy?

Andy

I have heard of this before and the only way it could be cured was to replace the whole immersion heater. That cured it, the noisy one was faulty and the shop that supplied it replaced it.

Thanks. The immersion that was replaced was the Booster, which I am not using. The noise is coming from the main immersion which hasn't been replaced. The replacement was an off the shelf model - no idea of the cost as this is being done on insurance. Have switched the whole system off until the thermostat is replaced, but fear that the noise will occur again as soon as the immersion is switched on.

Why on earth replace something you never use?
A 21/4" plug would have been a few quid.

Edit; just noticed it's an insurance job.