They mean not much under law. If you had a failure 1 week after a
guarantee
expired, a court would go in your favour. I think "fit for purpose" is
the
term.

Not quite. It would be under "satisfactory quality" (which replaced
merchantable quality a while back). Obviously, the pump is fit for purpose
(when it works) as it pumps water, which is its purpose. A fit for purpose
claim would be because when you opened the box, you got a thermostatic
radiator valve rather than a pump. That obviously would not be fit for the
purpose of pumping water.

Christian.