T11 pump stuck on?

MY Tii has the pump stuck on, I am isolating it via the fused connection, but it will not clear.
Is it likely to be a simple stuck float switch or is there a different switching process? Is there likely to be a problem with replacing the o-ring or seal if I carefully lifting the top, it is a few years old, and where might I get replacement parts if required?

Iain J
November 2010