Just found out out from my new tenants that there is no immersion fitted in the insulated copper cylinder,imersion switch is installed and lights up.My plumber does not seem to interested in sorting us out.My question, would it be too big a job for myself to go at,im quite handy at the DIY and the immersions seem reasonable enough to purchase.Is it worth my while, myself and my DIY book to tackle this job or too best leave it to another plumber? Any help appreciated. Chippy