Rekeyed Lock Sticks Only in Cold After Pinning Decision Tree

Why this matters

A lock you rekeyed last week now sticks every morning and frees up by noon. The customer is convinced the rekey caused it, and on a same-week callback they are usually right that something you touched is involved. But "the rekey caused it" and "cold weather exposed a marginal condition you created" are two different diagnoses with different fixes. Getting this wrong means a second callback. Cold-only sticking points at three culprits that all live inside the cylinder you just had open: chip or burr binding on a pin, over-thick or contaminated lubricant that gels below freezing, and a pin stack height that was already marginal and goes out of spec when the cylinder body contracts. Work them in order and you fix it on the first return trip.

Symptom presentation

The defining trait is temperature dependence. The key enters and turns smoothly when the lock is warm but binds, drags, or refuses to turn the last few degrees when ambient temperature is near or below freezing. The customer often reports it is worst at first use of the day and clears after the door has been worked a few times or the sun hits it. A lock that sticks at all temperatures is not this problem; that is a pinning or alignment fault and belongs to a different tree. Confirm the cold dependency before you spend time here: ask whether it ever sticks in the afternoon, and check whether an interior lock at the same temperature behaves differently from an exterior one.

Quick checks

Run these before pulling the cylinder.

• Operate the key with the door open so the bolt is free of the strike. If it still binds with no strike engagement, the fault is inside the cylinder, not at the strike or alignment, and the rest of this tree applies.
• Try a freshly cut key off the original, not the customer's worn copy. A worn or miscut copy that drags in cold has nothing to do with your pinning, and ruling it out first saves you from re-pinning a cylinder that is fine.
• Feel for the bind point. Sticking on key insertion or withdrawal points at a pin chamber catching; sticking only on the turn after the plug starts to rotate points at lubricant drag or, on a high-security cylinder, a sidebar or secondary element not releasing.
• Note whether the same cylinder you rekeyed is the one that sticks, or an adjacent lock that was never touched. Customers conflate them, and a cold-sticking lock you never opened is not your callback.
• Compare an interior lock at the same indoor temperature to the cold exterior one. If only the cold exterior cylinder drags, the temperature dependence is confirmed and you can stop looking for a temperature-independent pinning fault.

Isolation tree

Start at the plug and work outward.

Branch 1: Does it bind on key insertion or extraction, before any turn? Pull the plug and inspect each pin chamber under magnification. Look for brass curls or burrs at the chamber mouths left by a worn key gauge or a chipped pinning tool. Cold tightens clearances and a burr that cleared at room temperature now catches. Deburr the chamber and re-pin with new bottom pins. This is the most common true root cause on a same-week cold callback.

Branch 2: Does it bind only after the plug starts to rotate, with a gritty or sluggish feel? Suspect lubricant. If you used a wet oil or a grease, it gels in cold and adds drag the springs cannot overcome. Flush the cylinder with a non-residue cleaner and relubricate with a dry-film PTFE or graphite product rated for the climate. Wet lubricants belong nowhere in a pin-tumbler cylinder.

Branch 3: Binds on the turn, clean and dry inside, key cuts verified correct? Check pin stack heights against the bitting. A bottom pin one increment too tall sits the stack slightly proud of the shear line; at room temperature the spring and bevel let it ride through, but a contracted plug-to-body fit in cold removes that margin. Re-measure with a pin gauge and drop the offending bottom pin one step.

Branch 4: High-security cylinder with a sidebar (interactive element, finger pins)? Cold-sensitive sidebar engagement usually means the secondary element spring is weak or the element is gummed with the wrong lube. Treat as Branch 2 first, then inspect the element.

Confirming diagnosis

You have the right cause when the corrective action survives a cold re-test. The honest field method: chill the rekeyed cylinder. Leave it in an unheated vehicle or against an exterior wall until it reaches outdoor temperature, then operate it. A plug that turns with the same light, even torque cold and warm is fixed. A bench test at room temperature proves nothing on a cold-only complaint. If you cannot wait for ambient cold, a short blast from a canned-air duster inverted to spray liquid will frost the cylinder enough to reproduce drag on a marginal stack.

Remediation

• Burr or chip (Branch 1): deburr chambers, replace affected bottom pins, verify smooth gauged insertion, relube dry.
• Lubricant gel (Branch 2): flush, dry-film lubricant only, work the plug 20 cycles to distribute.
• Marginal stack (Branch 3): drop the proud bottom pin one increment, confirm shear-line flush with a follower and key, cold-test.
• Document the corrected pinning. On a keyed-alike system, apply the same correction to sister cylinders pinned in the same session so you do not chase the same callback across the building.

References

• BHMA/ANSI A156.5, Auxiliary Locks and Associated Products (cylinder and deadbolt performance criteria).
• BHMA/ANSI A156.115, Hardware Preparation in Steel Doors and Frames (clearances and fit affecting bind).
• Schlage Commercial Locks Technical Reference and Pinning Charts (bottom-pin increments and stack heights).
• Kwikset SmartKey and standard cylinder rekey service documentation (pin gauge use and lubrication guidance).