Depending where is has broken off, depends to what extent of how much you will have to replace, but worse case scenario is, inside there is a cartridge that has a little lever that the diverter handle attaches too. This whole cartridge needs to be replaced. Depending on the make, it can be costly.
depending on your spout diverter if its a valve or is it on the spout it self, if the diverter is on the spout then your diverter is not letting full flow of water out of the spout and its putting enough pressure to allow the water out of the shower head, I had this problem before and if you change the spout it should fix the problem. If you have a 3 way valve which is on the wall then i would suggest replaceing the parts in that valve if possible other wise change out the divert valve. If your broke like me and want a cheap fix then put either a water flow resistor or a shutoff right before your shower head.
The tub spout diverter,is just worn out.Go to your plumbing or hardware store and buy another with the same installation properties.(You may want to remove the old one to see how it was installed)
“DO YOU FIX DENTURES THEY BROKE IN HALF”
some lady said if it anit broke don't fix it
To fix a Jaguar S type heater, check the diverter mechanism. It shunts air through the heater core, which may not be operating properly.
fulcrum
If It Ain't Broke...
fix her
If it is coming from the tub spout then the gasket is moving around or esle it is shot. The easiest way to fix this is to get a new tub spout. It will more than likely take more time to attempt to change the gasket on the spout then to install a new one.
Fix it
Then fix it retard.
Replace it with a new one.