If what the correspondent really meant was that the pumps weren’t working, or were the wrong kind for the job, then “redundant” is certainly not the right word to cover either situation.
In the UK, sacking an employee is now a very difficult and long-drawn-out process; unless they are obliging enough to commit some truly spectacular and criminal misconduct meriting summary dismissal you have to go through a long and painful process involving verbal warnings, written warnings and so on. And at the end of it, the employee can take you to an industrial tribunal and if you haven’t carried out every single aspect of the process perfectly they can take you to the cleaners. For this reason many employers prefer to reorganise the workplace in such a way that the problem employee’s job becomes (however technically) redundant. Redundancy carries with it a compensation payment meant to ease the period of looking for another job, and, of course, no blot on the worker’s record, so most problem employees will go quietly if offered it, and employers reckon the money is well spent.
So redundancy is indeed routinely used as a legal ploy for getting rid of workers you don’t want, but it still is not the same as sacking them. The very availability of fig-leaves such as “redundancy” or “ill-health retirement” have made actual sackings a relatively rare and dramatic event.