I have just had central heating fitted.
The new boiler has a leak. It has gone into the control panel.
A fitter is coming out from the company that make it on mon morning.
Do i have to accept him repairing it. Or should it be replaced?

If its been damaged by water and he "repairs" it then he will basically have replaced it, no-one sits down with a soldering iron to repair circuit boards these days, especially not field service engineers.

Depends upon what leaked and from where.

If it was an ill fitting joint/compression fitting they may just change the part. They certainly should replace the control panel. Anything else, they should consider replacing the unit as these are pressurised units and there are regulations concerning them, plus any reputable company will find it in their best interest, and insurance liability to consider replacement.

Cheers guys for your help.
It appears to be leaking from the pump.