Air is leaking through trigger when trigger is not depressed. When trigger is depressed and nail tail cover is in safety position (holding gun in air) it completely stops. The gun fires well but there is just a significant amount of air escaping when trigger is not depressed. Could it be the valve packing near the urethane ball in trigger?

Try ez test to check for proper operation. Remove nails and air supply, point nose of gun up then down again. The driver should not move from the top of cylinder position. If driver is moving up then down replace the driver oring. If driver oring seems ok then connect air supply and bump fire the nailer without nails against soft wood and door open so that you can see the driver and feeder moving. Bump fire the gun and make sure that the driver is moving all the way back up to top of cylinder and the feeder is moving rapidly back and forward. If movement seems ok then hold the nose down on soft wood and depress and hold the trigger. This will fire the gun but driver will stay at the bottom position and not return until you release the trigger or lift the gun. When holding the gun with the driver down position, no air should leak out the top or bottom of the gun. If air leaks out bottom, replace lower bumper, if air leaks out the top replace the upper bumper. Good luck

Easy to check. Remove nails from gun and connect to air supply. Using hard rubber pad or soft wood depress and hold trigger and push nailer safety against pad and hold there. The gun will fire but the driver will stay down until you pull back on the gun and relieve pressure on the safety foot. With driver down examine the tip of the driver. It should look square and should extend about 1/4 inch or more past the nose. If tip is broken replace driver. If lots of air is leaking past the nose during test, also replace the lower bumper. Good luck

Most nailers have a two position setting on the trigger to allow for single fire or bump fire. If set on bump fire, the gun will work better when you bump fire the gun instead of placing the gun on the work then depress trigger. Bump fire works best when safety spring has good tension. Easy test. Make sure that the safety spring is in place (with air hose removed, contact foot should spring back quickly when pushed against work). With air connected, hold trigger and quickly bounce the gun against the work. If the gun does not fire when you bump, the trigger is most likely set to single fire. With trigger set to single fire, you must place the gun against the work, then depress trigger. If the gun shoots two nails while set to single fire, most likely worn trigger or worn out trigger valve. These parts are not expensive and are easy to replace. Good luck

If the new trigger valve leaks air when you connect the air supply, most likely defective valve or air is leaking past outer trigger valve orings due to debris in the slot or new orings were cut when the valve was pushed in. If air leaks when you depress safety to fire gun then most likely problem is in the head valve or safety foot is not pushing the firing pin all the way in. Easy test, remove nails and remove the trigger to expose the firing pin. Connect air and very quickly depress the firing pin all the way in. If the gun fires, adjust the safety foot as needed. If the gun does not fire, remove the head and check headvalve orings for good snug fit against the cylinder within the head. The surface were orings make contact must be very smooth and not too deeply worn. If you notice fine scratches remove with fine sandpaper. Reinstall head using plenty of white grease on all the orings within the head and retest. Good luck

Check the safety trip make sure it is pushing back far enough. If it doesn't then it won't do anything. When it was fine just moments earlier.

Safety foot and lever inside of trigger are not pushing the trigger pin all the way in. To verifty that the gun will fire, remove the nails to allow for dry fire. Remove the trigger to reveal the trigger valve. Hold the gun against old coiled rubber hose or soft wood. Very quickly depress the trigger pin all the way in. If the gun fires, adjust safety foot and trigger so that the trigger pin is fully depressed when your bump fire. If the gun will not fire after adjustment, remove the head and lube headvalve/orings with silicone paste lube.

The gun will miss fire if the driver does not return to top position allowing nails to move into position. Could be bent driver, faulty trigger, cracked lower bumper or check valve not in place. Easy to check if trigger. Remove air supply, and remove the pin holding the trigger. Fire the nailer by depressing the firing pin with your finger. If the gun works ok, single fire trigger is faulty or safety foot is out of adjustment. If still miss fire, remove head and pull out cylinder and piston. Check for bent driver, cracked lower bumper or black band (check valve) is out of place on outer part of cylinder covering a row of holes.

There are about three issues with this gun that could cause your problem. The safety contact arm not depressing the trigger pin fully, worn trigger valve (tva6), or leaking orings in the headvalve. Easy tests. Remove the nails, and remove the trigger to expose the tva6 valve. Reconnect air and with very quick and firm action, depress trigger pin all the way in. If the gun fires, adjust safety foot and trigger so that the trigger pin is depressed all the way in each time that you fire the gun. If the gun does not fire, remove the head and remove the headvalve. Examine the surface/s where Orings make contact with magnify glass looking for fine scratches. Sand with 400 grit paper. Orings must make good contact here or gun will not fire. Lube orings and surface with silicone paste lube (sold at Lowes in the plumbing department or swimming pool supply store). If no fine scratches and surface looks smooth, replace Orings in head and the tva6 valve. Good luck with your repair/

Remove the nails and air supply. With side door open notice position of driver. Driver should be at top position with tip not visible. If driver is down and it moves within cylinder when you tilt nose up then down again, time to replace orings. If driver is down, it should extend past the nose about 1/4 inch (if driver is broken at the tip the end will look rough and nail will not drive in all the way). If driver extends past the nose more than 1/4 inch then lower bumper may be breaking up /cracked. Easy test for proper function. With nails removed and side door open, connect air to gun and dry fire gun against hard rubber or old coiled air-hose (with air connected and trigger depressed, no air should leak from trigger area, if air leaks when trigger is depressed, look for fault at trigger pin). Feeder should move back then forward in quick motion almost matching speed of driver and driver should not creep down between shots. No air should leak from nose of the gun (push nose against hard rubber and depress trigger and hold in this position, driver should stay down with very little or no air leaking out of nose, when you release trigger, driver will return). If air leaks out of nose while holding in this position, replace lower bumper. If a quantity of air leaks from valve in front of trigger, cylinder orings may need replacing or outer part of cylinder has fine scratches (remove scratches with 400 grit paper). Parts are available at www.toolpartsdirect.com. Good lucki

get a senco