Quick Answer: A grease gun stops pumping because of an air lock, wrong grease consistency, a worn plunger seal, a clogged Zerk fitting, or a coupler that cannot engage. Start with the 5-point checklist below.
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Common fixes: replacement Zerk fittings · locking grease coupler · cordless grease gun.
Common Symptoms of a Failing Grease Gun
- Handle or trigger moves but no grease exits the coupler.
- Gun pumps briefly then loses pressure on every stroke.
- Grease leaks from the head or cartridge area instead of the coupler.
- High resistance followed by sudden blow-off from the coupler.
Quick Diagnostic Checklist
| Check | What to Look For | Most Likely Cause |
|---|---|---|
| 1. Cartridge / reservoir | Empty, collapsed, or improperly seated cartridge | Empty cartridge detection failure |
| 2. Coupler engagement | Coupler slips or leaks around the Zerk head | Worn fitting or wrong coupler type |
| 3. Grease condition | Separated, hardened, or wrong NLGI grade | Wrong grease consistency |
| 4. Pump action | Spongy or uneven stroke | Air lock or worn plunger seal |
| 5. Zerk fitting | Blocked or damaged fitting | Clogged Zerk / blocked lubrication point |
Cause #1: Air Lock in the Grease Gun
Air trapped in the pump head compresses instead of moving grease. Bleed the gun by loosening the head one turn and pumping slowly until grease appears at the threads, then retighten. For cartridge guns, ensure the cartridge foil seal is fully pierced and the follower plate is seated against the grease.
Cause #2: Wrong Grease Consistency / NLGI Grade
Thicker grease is harder to pump, especially in cold weather or with long hoses. NLGI #2 is standard for most bearings; NLGI #1 or #0 flows more easily in cold conditions or through small-bore lines. Do not mix greases with incompatible thickeners—this can cause hardening or separation inside the gun.
Cause #3: Worn or Damaged Plunger Seal
The plunger seal creates suction on the return stroke and pressure on the power stroke. A cut or hardened seal allows grease to bypass internally, causing weak or no output. Replace the seal kit for your gun model and re-grease the plunger lightly during reassembly.
Cause #4: Clogged Zerk Fitting / Blocked Lubrication Point
Hardened grease, dirt, or corrosion can block the Zerk check ball or the internal passage. Remove the fitting and test flow with the coupler held in free air. If the gun pumps freely, the blockage is in the fitting or bearing. Replace the Zerk fitting and clean the port before reinstalling.
Cause #5: Empty Cartridge Detection Failure
Some battery and pneumatic guns have low-grease sensors or follower plates that can stick. Check the cartridge visually, confirm the follower plate moves freely, and reset or reseat the cartridge if the gun has a cartridge recognition switch.
Cause #6: Faulty Coupler Not Engaging
Standard push-on couplers slip on worn or high-back-pressure fittings. A 4-jaw locking coupler rated to 12,000 PSI grips the Zerk head mechanically and eliminates blow-off. For badly worn fittings, a double-handle locking pliers coupler provides 3× the grip force of a push-on style.
When to Replace vs. Repair Your Grease Gun
| Issue | Repair | Replace |
|---|---|---|
| Worn seal | Seal kit replacement | — |
| Clogged coupler | Clean or replace coupler | — |
| Cracked barrel or head | — | Gun body |
| Stripped threads | — | Head or coupler |
| Motor failure (battery/pneumatic) | Diagnose power source | Motor or entire gun |
Frequently Asked Questions
Why does my grease gun pump air but not grease?
This is usually an air lock or an empty cartridge with residual air in the head. Bleed the gun and confirm the cartridge is full and properly seated.
Can cold weather stop a grease gun from pumping?
Yes. NLGI #2 grease stiffens significantly below 0°C and may not flow through small coupler bores. Switch to NLGI #1 or #0 grease for cold-weather operation, or store grease cartridges indoors before use.
Why does grease leak from the gun head instead of the coupler?
The head seal or plunger seal is worn, or the head is cross-threaded. Inspect and replace the seal; do not over-tighten the head.
How do I know if the Zerk fitting is blocked?
Remove the fitting and try pumping into free air. If the gun works without the fitting, the Zerk or bearing passage is blocked. Replace the fitting and clean the port.
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