L-bar sealer troubleshooting
Fixes for weak seals, burn-through, film sticking, dog ears, fish eyes, and ballooning, plus routine maintenance and parts, from manufacturer manuals.
Use this guide to find out why a seal or shrink fails and what to try. For cleaning, wear parts, and spares, see routine maintenance. For repeatable product settings, keep a setup record.
Before you adjust anything
Change one setting at a time. Run a few packages after each change. If you change several settings at once, you can’t tell which one fixed the problem.
Before you touch any parts, follow the maker’s steps to shut down, cool, and isolate energy. Turning off a control switch does not isolate energy. Automatic machines may store air pressure (pneumatic energy) as well as electrical power. Where it applies, follow your employer’s procedure under OSHA 29 CFR 1910.147. That procedure includes control of stored energy and verification. The standard has its own scope and exceptions. One exception covers certain cord-and-plug equipment under the servicing employee’s exclusive control. This page is not a complete lockout procedure.
Guards, interlocks, wiring, hot parts, and tensioned assemblies need the procedure and staff the maker specifies. Leave electrical work, heater replacement, and anything behind a guard to a qualified technician. Eastey’s manual says to “use only licensed electricians to check or repair electrical wiring”. Your machine’s manual overrides anything on this page.
Machine or film? Clysar suggests a one-minute test. Seal an empty bag at your current settings. If the empty bag seals well, look at film sizing or product loading. If it seals badly, look at your settings and the condition of the seal system. Treat the result as a clue, not proof of one cause.
Seal problems
Check the seal before blaming the tunnel
If packages fail in the tunnel, first make sure the seal was good when it left the sealer. Start with the empty-bag test. Then look at a seal from a package that has not been through the tunnel. These signs come from Clysar’s troubleshooting tips:
- Gaps or voids along the seal. Have seal pressure and jaw alignment checked with the maker’s approved procedure.
- Small, brittle seals with pinholes, or white lines about 1/16 in. beside the seal. The seal is too hot.
- A jagged seal that looks torn, or film that doesn’t cut off. The seal is too cold.
If the seal looks good leaving the sealer but fails in the tunnel, Clysar says to check the package first. Reduce film tension at the seal, add or move perforations, or use a larger bag. Then check the tunnel settings.
In the table below, dwell is how long the seal bar stays closed on the film. PTFE tape is the nonstick tape that covers the seal wire and pad.
| Symptom | Likely causes | What to try |
|---|---|---|
| Weak or open seals | Seal temperature too low. Dwell too short. Film pulled tight at the seal. Dirty seal wire or knife. Worn PTFE tape or seal pad. Uneven hold-down pressure. | Raise temperature or dwell in small steps. Keep the bag loose and set the table so the seal falls at half the package height. Clean the seal element. Replace worn tape or pads. |
| Brittle seals with pinholes, or white lines next to the seal | Seal temperature too high. Clysar calls excess heat “the leading cause of seal failure”. | Lower the temperature. Clysar’s method: step down until the film stops cutting, then raise 5 to 20°F until seals are consistent. |
| Burn-through or charred seal | Temperature or dwell too high. Worn pad. Too much head pressure. | Lower temperature or dwell. Check the pad and pressure. |
| Seals blow out in the tunnel | Film too tight at the seal. Not enough perforation, so air can’t escape. | Leave more slack in the bag. Add perforation or use a larger bag. |
| Film sticks to the seal head, smoke, or buildup | Worn or dirty PTFE tape or pad. On knife sealers, buildup on the knife means it is running too cool. Smoke and buildup on the pad mean too much heat. | Clean or replace tape and pads. Adjust temperature in the direction the buildup points to. |
| Stringy cut (“angel hair”) or incomplete cut-off | Temperature wrong for the film. Dirty or nicked wire or knife. Worn pad. | Check the film maker’s troubleshooting guidance before changing heat or dwell. Stringing does not point to one universal temperature fault. Inspect and service the sealing surfaces and pad using the machine manual. |
| Seal is off-center on the package | Table or platform height | Adjust the platform so the seal sits at half the package height. |
| Gaps or dotted sections in the seal | Uneven jaw pressure, or a worn or misaligned pad | Clysar describes a paper-impression check for jaw pressure. Use it only if the machine maker approves it. Have qualified service staff correct uneven pressure or alignment. |
Sources: Eastey EM manual, Heat Seal HS-1620 manual, Sealer Sales SS-1622HK manual, Clysar troubleshooting tips.
Shrink and appearance problems
| Symptom | What it looks like | Likely causes | What to try |
|---|---|---|---|
| Dog ears | Unshrunk flaps of film at the corners | Too much film. Not enough perforation. Not enough heat or air at the package ends. | Use a smaller bag and add perforation. Slow the conveyor, raise tunnel heat, and aim airflow at the ends. |
| Fish eyes | Small round spots that didn’t shrink | Film touches the product and cools before the rest has shrunk. | Raise tunnel temperature and use less film. Sources disagree on conveyor speed: Clysar says speed up slightly, Heat Seal says slow down. Use your machine and film supplier’s procedure to settle it. Don’t treat either direction as universal. |
| Crow’s feet | Wrinkles radiating from the corners | Not enough heat, or too much air escaping at the corners | Slow the conveyor, raise tunnel temperature, and use fewer perforations or move them. |
| Severe ballooning or bags burst | Bag stays puffed up through the tunnel or bursts | Not enough perforation, a worn perforator, or a tunnel that is too cool | Some ballooning mid-tunnel is normal. Clysar says the bag should collapse about ¾ of the way through. Check the perforator position and pins. Use pre-perforated film. Raise tunnel temperature. |
| Burn holes or whitened film | Holes or white patches after the tunnel | Too hot or too slow in the tunnel. Film touching the tunnel walls. Air aimed at one spot. | Speed up the conveyor or lower the temperature. Check package clearance and airflow direction. |
| Loose or uneven shrink | Film still slack after the tunnel | Tunnel too cool, conveyor too fast, blocked air screens, or missing tunnel curtains | Slow the conveyor or raise heat. Clean intake screens. Keep curtains in place. |
| Cloudy film | Haze on the finished pack | Overheated film, or condensation on cold or moist products. Clysar’s ABL data sheet says that film begins to cloud as it approaches overheating. | Lower tunnel heat. Use an anti-fog film for refrigerated or fresh products. |
| Crushed or bent product | Package deforms as the film shrinks | Film shrink force too strong for the product | Use a larger bag, less heat, or less airflow. If that fails, switch to a low shrink-force film. |
Sources: Clysar package appearance tips, Clysar troubleshooting tips, Heat Seal HS-1620 manual, Seal-A-Tron tunnel guide.
Film handling problems
| Symptom | Likely causes | What to try |
|---|---|---|
| Film clings together or shocks operators | Static | Stop and have electrical safety checked if operators get shocks. Don’t assume every shock is static. Ask about approved static control if film cling is the issue. |
| Layers on the roll stick together | Film stored too hot | Store film at 90°F or below. |
| Film drags or won’t feed | Threading or film brake too tight | Check threading, loosen the film brake, and make sure guide rollers turn freely. |
| Film overruns or spills off the roll | Film brake too loose | Tighten the film brake. |
| Film splits along the fold | Damaged roll or product tray position | Check the roll edges and the product tray setting. |
Machine problems
| Symptom | Operator checks | Call a technician if |
|---|---|---|
| Seal head won’t stay down | Check the allowed operator controls and dwell setting against the manual. Magnet-gap and switch checks are model-specific service steps, not general operator tests. | The head still won’t hold, a fuse has blown, or the manual calls for a part inspection. |
| Wire or knife doesn’t heat | Check the plug, outlet, power switch, and that the seal timer isn’t at zero. | The display is on but nothing heats. Heating elements should be replaced by qualified technicians. |
| Front and side bars heat unevenly | Compare each controller with the approved recipe. Some models and films use different side and cross-seal settings. Don’t force equal values unless the manual says to. | Wiring or thermocouple inspection is needed. |
| Takeaway conveyor won’t run | Check the operator timer and displayed faults against the manual. Don’t work switches by hand or reach into the conveyor. | The motor or controls have failed. |
| Tunnel won’t reach temperature | Confirm the set temperature, clean intake screens, and check that the blower runs. | Heaters, relays, or the blower need diagnosis. Never replace a fuse with a higher rating. |
Routine maintenance
Start with the exact model, serial number, and manual. Impulse-wire and constant-heat knife sealers use different parts and service steps. Follow the safety steps in before you adjust anything for every task here.
Use your manual’s intervals, not a universal daily or weekly plan. The tasks below come from Eastey, Heat Seal, and Sealer Sales manuals. The Heat Seal HSE-100 manual is one example. It has a cleaning schedule and separate steps for pads and wires. Its methods apply to that system only.
At the intervals in your manual
- Clean the seal element as your manual says, after power-off and cool-down.
- Heat Seal says to clean a hot-knife seal bar with a soft dry cloth only. Clysar suggests scrap film.
- Never use abrasives on a knife. They damage its coating.
- Heat Seal says to clean seal wires with a soft brass wire brush.
- Check the PTFE tape and seal pads for tears, burns, and melted film.
- Wipe the product tray. Inspect tunnel rollers and belts.
Scheduled service checks
- Check seal head alignment and pressure.
- Clean tunnel intake screens and airflow holes.
- Confirm the seal bars and tunnel hold their set temperature.
- Check conveyor belt and chain tension.
When worn
- Replace PTFE tape before it burns through. Sealer Sales calls it “the item most subject to wear”.
- Replace seal pads when seals show gaps, cut-off gets worse, or you need more pressure to seal.
- Put on new PTFE tape when you replace a seal wire. Uline’s H-2378 manual ends its wire replacement steps with new tape over the wire.
For sealers with a temperature control, find the lowest approved setting that gives repeatable, good seals. Impulse sealers may control heat with a timer instead of a temperature setting.
Identify parts before ordering
A replacement that looks the same length may have the wrong electrical or material spec. Give the supplier the details below.
| Part | Information to give the supplier | What to record during an approved inspection |
|---|---|---|
| Impulse sealing wire or ribbon | OEM part number, machine serial number, side or end position | Breaks, buildup, where it keeps failing |
| PTFE tape | OEM grade, width, thickness, adhesive or backing spec | Burns, lifting, tears, residue |
| Seal pads | OEM material, profile, dimensions, mounting | Grooves, burns, uneven support |
| Hot knife or cutting rule | Model, revision, coating, matched insert or holder | Damage or coating wear found under the service procedure |
| Belts, magnets, sensors | Assembly part number and machine setup | Tracking issues, uneven holding, or repeat faults |
The Uline H-2378 manual warns that the wrong replacement element can damage the transformer. It also ties seal quality to seal-pad wear and tape cleanliness. Don’t choose generic wire by its length alone.
Keep a maintenance record
Record these fields for each task:
- Date, machine model, serial number, and operating hours or package count if you have them.
- Manual revision and the task done.
- Condition found, part number installed, and who did the work.
- Film spec and settings used for the test run.
- Result before shrinking and after the finished package cooled.
- Any repeat fault and the next step agreed with service support.
Buying a used machine? Pair these records with the used-machine inspection checks.
Keep useful spares
Ask the maker which consumable kit matches your serial number. Ask which failures need a technician. Record stock on hand, supplier lead time, and replacement cost. Before you buy a machine, get spare part numbers and prices in writing, as the support questions in the buying guide suggest. A cheap spare with a long delivery time can matter more than a big box of parts that don’t fit.
Find the cause before you fit more parts if a wire keeps failing, one corner stays weak, or film still sticks after cleaning. Use the tables above. Give service support the failure location, film details, photos, and maintenance history. After a repair, do the checks the maker requires and keep samples from the test run.
When to call for service
Contact the maker or a qualified service provider if the steps above don’t fix the problem. Do the same for any problem with electrical parts, heaters, or anything behind a guard. The Eastey manual separates maintenance tasks and calls for qualified electrical service. This page helps you find and record the work. It doesn’t replace your model’s repair procedure.
Have these ready when you call:
- Model and serial number.
- Film type and gauge.
- Your seal and tunnel settings.
- When the problem started.
- A defective sample next to a good one.