If your airless spray pump primes and pressurises but nothing happens when the trigger is pulled, and it is not the airless spray tip that is blocked, the actual spray gun hand piece could be where the problem is located.
The first thing that needs to be done is relieve all pressure from the airless spray system by opening the prime spray or bypass valve and turn the machine off.
If the airless spray gun has a built-in paint filter this needs to be checked. Many airless spray guns incorporate a paint filter in the handle. There is usually a point where the trigger safety guards can be detached so the handle can be unscrewed from the airless spray gun. More often than not it will be found that the airless spray gun paint filter is either completely blocked or has been put in backwards which also blocks all paint flow through the spray gun.
If the airless spray gun paint filter has been completely blocked it may be easier to simply replace the entire filter with a new one rather than trying to clean the blocked filter as the filter mesh will almost always have been collapsed by the pressure. The paint filters in airless spray gun handles can even become blocked so extensively that the filter cannot be easily removed from the airless spray gun handle. This situation may require removal of the hose swivel so a suitable tool can be used to drive the blocked filter from the spray gun handle.
If the airless spray gun blockage has been caused by the paint filter being inserted into the gun backwards some filters may come apart or even break off leaving the paint flow port into the spray gun head blocked with plastic. This may require long nosed pliers or other similar tool to try and remove the obstruction.
Another cause of blockage in an airless spray gun handpiece could be dried paint and if this is the case it is quite possible that much more than just the airless spray gun handle is affected. Assessment will need to take place to determine if the estimated time and cleaning solvents to rectify dried paint blockages throughout an airless paint system will be worth the cost compared to replacement with new components.
Another very rare cause of airless spray gun handpiece blockage that has been observed in the past is where the actual ball is not fitted tightly enough in its holder so when the airless spray gun trigger is depressed with pressure inside the spray gun the ball seperates and remains pressed in the seat while the rest of the needle and spring set operate as normal. When the trigger is released the ball is returned to the needle and spring set assembly so when the airless spray gun is dismantled nothing untoward is noticed. Once again this actual problem is very rare but could be something to check if all other diagnosis fails to locate the cause.