It runs when u press the trigger theres no fire or air comes out

The trigger valve should release air when depressed. This release of air comes from behind the head valve. If the head valve does not pup-up when the trigger is depressed then air is leaking past the head valve orings. Try coating the head valve orings with plenty of white grease and retest. If the gun fires you know that orings are leaking. Test with no more than 100 psi. Good luck with your repair.

Could be lack of lubricant or safety foot not pushing trigger valve pin all the way in. Easy to check. Remove nails and remove trigger to expose the trigger valve firing pin. Connect air and with very quick action depress the firing pin all the way in with finger. If gun fires adjust safety so it pushes on trigger pin completely. If no fire, remove head and head valve and apply plenty of white grease or silicone paste to orings and reassemble for retest. Good luck

while I have to say I am not a dewalt guy, I can try to point you in the right direction, assuming there are no leaks, then you state the trigger is not engaging , could be three things, one the trip ( safety) or the trigger valve or the trigger its self, if you feel comfortable pound out the pit that holds the trigger in. Just the trigger not the valve, then activate air to the gun, press the trigger, if it fires its the trip or the trigger rocker switch. the trigger can be examined see if its damaged bent or cracked, see if the safety trip is out of adjust, if it doesn't fire it could be the valve spring inside the trigger valve is broken.
don't worry just watch how it comes apart and remember you cant make it worse. it doesn't fire now. anything is an improvement

Remove the head and lube the headvalve with white grease. If gun still does not fire and makes air noise at the trigger valve then orings within the trigger valve are worn. Replace the trigger valve or if you have a source for small orings, just replace the two orings on the metal stem (2mm x 1.5mm). Dewalt uses vinyl orings on the stem that fail. Replace with buna. Good luck

Not all nailers have the ability to bump-fire. It depends on the type of trigger and the firing valve that the trigger contacts. Remove gun from air supply and remove the nails (for safety). Take a close look at the trigger itself looking for a bump fire setting. It will have a rotary dial to select single or repeat fire. If no setting, look at how the safety foot contacts the trigger's inner trip lever (the trip lever inside the trigger is what actually contacts the firing valve pin). With trigger pressed in, push the safety foot in and notice if the safety contacts the inner trigger lever. On bump fire trigger, the safety foot mech. will push up on the inner lever each time that you press in safety (and you will see that the inner lever will depress the firing pin). On single fire trigger, with trigger pressed, when you push on safety foot, the mech. will not contact inner trigger lever because the lever is too short to allow safety to make contact with it. On single fire triggers, the inner lever can make contact with safety only when trigger is in the resting position. With trigger released, depress safety and notice that safety contacts inner trigger liver and will remain in contact untill you press the trigger at which time the inner lever will depress the firing pin then fall away from safety. If you are a tinker-er, you can make adjustment to inner lever so that it will make constant contact (the rotary dial on triggers that are made to give you a choice of bump or single actually make the inner lever longer or shorter ). If you make any adjustments, make various and numerous tests with-out nails to make sure that it will not fire accidently.

Remove nails and remove trigger to expose trigger valve pin. Place nose of gun against rubber pad or old coiled up air hose to absorb impact of driver and with very quick and deliberate motion press in trigger pin. If gun fires, then problem is with safety foot not pushing trigger pin all the way in (or worn trigger). Make adjustment as needed or replace faulty parts. If gun still does not fire, then likely problem is with headvalve. If headvalve orings are leaking, gun will not fire. Test for leaking orings as follows. Remove head and remove headvalve, apply silicone paste lube (plenty) to all orings and where orings contact. Assemble and do test above. If gun fires then surface where orings contact is allowing air to leak(smooth with very fine sandpaper if scratched).

On some models the contact fire is not available. There is a flap that is under the actual trigger. When you press the safety in, it engages this little flap which allows the trigger to be engaged. As soon as the safety comes up this little flap falls back down disengaging the trigger.

There is an optional trigger assembly that you can put on this nailer. You need parts 174299 and 174300 to make this gun a contact nailer.

They all leak a little on firing. Is it a big blast of air or just a hiss? All guns have a 'safety' device that keeps them from firing unless you follow a set pattern. You must push the gun down where you intend to put the staple which releases the safety before you pulll the trigger. You must then release the trigger move the stapler off the piece push it back down again before you can fire another staple. You can get (free) frrom the manufacture a rapid fire shoe and trigger that allows you to hold down the trigger and bounce the stapler along your work shooting merrily away.

get a senco

On most all nailguns when the trigger is activated air pressure is released from the headvalve causing the headvalve to open and fire the piston. If air leaks through the headvalve orings or through the headgasket port to headvalve, it will not fire. Try applying light grease to headvalve orings and make sure that headgasket is sealing around vent hole. If it fires then replace orings in headvalve for long term repair. Secondary problem is worn safety parts and trigger or trigger pin. If these parts are worn the trigger will not push the trigger valve pin all the way in when you bump fire the gun. With air supply disconnected, apply pressure to safety while depressing the trigger and check thet the pin is moving all the way into the trigger valve. Adjust or replace as necessary. Enjoy