Unless I've misread your post, I'm assuming that you mean an alternative to the €800 cost of replacing the pump rather than the alternative of replacing the system.
We've got a Soliflow system (same thing as a Desjoyaux) and are on the 3rd pump in 10yrs!! This latest one is 2 yrs old and much more powerful than the other two - when it works, it does the job well enough, but you always have the nagging feeling .............
So, 3wks ago I re-fitted the pump, started it up and off it went ............. for two days. Then it seized. I was mortified at the certain cost of €800 and asked some French friends for help. Three of them came round, stripped it down, took away the offending shaft and bearing, and returned three days later. All back together again in half an hour and it cost me €17!
If you're able to pinpoint the problem, then the solution may be equally as simple. I've no idea how competent you are at these things, but if not at all, then taking it to a halfway decent electrician might at least give you a diagnosis. Friends are better still !!