Flow Wrapper Troubleshooting: 10 Common Faults, Their Causes & How to Fix Them
- PacMatix
- Nov 11, 2025
- 9 min read
Understanding Common Flow Wrapper Problems
Flow wrappers are among the most reliable packaging machines in the food and non-food sectors — but even the best units need occasional adjustment and care.
From chocolate bars to cookies, fresh produce to frozen goods, small alignment issues or sealing faults can quickly turn into wasted product, downtime, or damaged film.
These machines are built for precision, but they’re also known to be sensitive to setup. In fact, incorrect adjustment accounts for the vast majority of reliability problems — making proper setup, sealing checks, and maintenance routines critical to consistent performance.
In this article, we’ll outline the 10 most common flow wrapper faults and what usually causes them — from film pulling off the feed wheels to weak seals and registration drift — helping maintenance teams quickly identify and fix problems before they escalate.
Quick Overview: 10 Common Flow Wrapper Faults and Likely Causes
Fault | Likely Cause |
1. Film pulling out of feed wheels | Incorrect forming box setup or low film tension |
2. Product crushed in sealing jaws | Infeed timing or product spacing misalignment |
3. Cut-off length inconsistencies | Slipping film, or unstable tension, film obstruction. |
4. Wrinkles on longitudinal seal | Film tracking or forming box misalignment, accessive pressure |
5. Weak longitudinal seals | Low sealing temperature or poor wheel pressure, cleaning issues |
6. Weak end seals | Contaminated jaws or poor sealing jaw adjustments. |
7. Cutting issues | Blunt or misaligned knives. |
8. Temperature fluctuations | Faulty thermocouples or contaminated sliprings. |
9. Film tension problems | Brake settings or dancer arm adjustment. |
10. Registration faults | Slippage or incorrect bag length parameters, film tension |
Diagnosing and Fixing Flow Wrapper Faults
Understanding the root cause behind each symptom is the key to faster troubleshooting. Many flow wrapper problems share similar underlying issues, film tension, temperature control, or mechanical alignment, but the signs they show can vary from one product or film type to another.
Below, we’ll break down each of the ten faults in more detail, explaining what typically causes them and how maintenance teams can correct or prevent them before they lead to downtime.
1. Film Pulling Out of the Feed Wheels
Symptom:
During operation, the film slips or pulls free from the feed (pulling) wheels, stopping product flow or causing film to lose registration.
Likely Causes:
Film tension is too low.
The forming box setup is incorrect.
The film width is too narrow for the product path.
Typical Root Cause:
In most cases, this issue traces back to incorrect forming box adjustment. When the box is set too tight or off-centre, it restricts film movement and reduces contact pressure between the film and the pulling wheels. That slip quickly compounds as the wrapper runs, leading to loss of grip and eventual film release.
Fix / Prevention:
Verify the forming box alignment and ensure the film path is centred and smooth.
Increase film tension gradually while checking for drag on the unwind brake.
Inspect the feed wheels for contamination, wear, or insufficient pressure.
Confirm film width is suitable for the forming box setup.
2. Product Crushed in Sealing Jaws
Symptom:
Product becomes caught or crushed between the sealing jaws during operation, resulting in damaged packs, sealing contamination, or machine stoppages.
Likely Causes:
Incorrect infeed timing relative to jaw cycle.
Product spacing too tight or inconsistent.
Incorrect forming box adjustments
Infeed pitch not synchronised with sealing jaws. (Ratio)
Typical Root Cause:
Most cases stem from poor transfer of the product from the infeed pusher into the film tunnel through the forming box. On some machines where there are multiple pitches on the infeed, the infeed pitch may be set incorrectly for the bag length.
Often the product may be too loose in the film tunnel.
Fix / Prevention:
Review infeed speed and synchronisation parameters after any format change.
Check forming box adjustment are correct and that film is grabbing the product sufficiently.
3. Cut-Off Length Inconsistencies
Symptom:
Bag length varies during operation, with some packs cutting short and others long. The issue can appear intermittently, especially when running at higher speeds or after product changeovers.
Likely Causes:
Slipping film due to low or unstable tension.
Incorrect registration sensor sensitivity or positioning.
Insufficient feeding wheel pressure.
Mechanical play.
Typical Root Cause:
Most inconsistencies come from poor film control — either slipping on the feed rollers/wheels or fluctuating film tension between the unwind and the forming box. Even small variations in film stretch can throw off registration.
Fix / Prevention:
Check film tension and brake setting for consistent drag.
Inspect registration mark clarity and clean the sensor lens.
Check the feeding wheels are clamping and driving the film properly.
4. Wrinkles on Longitudinal Seal
Symptom:
Wrinkles appear along the longitudinal (centre) seal, often worsening as the machine warms up or when film rolls are changed. Wrinkles may cause poor sealing or visual defects on the finished pack.
Likely Causes:
Incorrect forming box alignment or worn former edges.
Film not tracking centrally over the forming box.
Excessive film tension or pressure from the sealing wheels.
Film roll not level or running off-centre on the unwind shaft.
Typical Root Cause:
Most cases are caused by poor film tracking through the forming box. When the film enters the box off-centre or at an angle, it twists slightly before reaching the sealing wheels — creating uneven pressure and wrinkles along the seam. Over-tensioning the film or excessive pressure on the longitudinal sealing wheels can make the issue worse, especially on thin or paper-based films.
Fix / Prevention:
Check film alignment at each roller and ensure it’s tracking straight into the forming box.
Inspect the forming box for wear or sharp edges and polish if required.
Reduce sealing wheel pressure and monitor film tracking stability.
Confirm unwind reel is level and tension brake isn’t over-tightened.
5. Weak Longitudinal Seals
Symptom:
The centre (longitudinal) seal does not bond properly, leading to open seams or seal separation when the pack is handled. This can appear intermittently or consistently, depending on film type and sealing temperature.
Likely Causes:
Insufficient heat or pressure at the longitudinal sealing wheels.
Dirty or worn sealing wheels.
Film contamination (e.g. oil, sugar dust, or crumbs on the seal area).
Incorrect film type or coating for the temperature setting.
Inconsistent film tension causing poor seal contact.
Typical Root Cause:
Weak longitudinal seals are most commonly caused by a loss of heat transfer between the sealing wheel and film. This may be due to buildup on the wheel surface, incorrect alignment, or running below the optimal sealing temperature for that film’s laminate. In some cases, unstable film tracking can cause uneven contact along the seal path, producing partial bonding.
Fix / Prevention:
Verify temperature setting matches the film specification (check with supplier data sheet).
Clean sealing wheels regularly to remove residue buildup.
Check sealing wheel alignment and pressure for even contact.
Maintain consistent film tension across the feed path.
If using paper or recyclable film, increase dwell time or switch to modulated heating control.
6. Poor End Seals
Symptom:
End seals appear weak, open, or contaminated. In some cases, the seal separates easily when the pack is handled or during drop tests. The issue may affect every pack or occur intermittently when product or film changes occur.
Likely Causes:
Insufficient sealing temperature or dwell time.
Excessive sealing pressure or misaligned jaws.
Product or crumbs caught between the jaws.
Film not suitable for current temperature settings.
Contamination from oil, sugar, or moisture on the film surface.
Uneven film tracking causing partial jaw contact.
Typical Root Cause:
Most poor end seals are caused by either incorrect temperature-pressure balance or contamination at the sealing area. When sealing temperature is too low, or film tension is unstable, the inner layers of the laminate fail to bond fully. Conversely, excessive temperature or pressure can over-melt the sealant, leading to brittle or distorted seals. Contamination — especially from crumbs, sugar, or oil — is a frequent cause in bakery and snack applications.
Field Note: One of the most common patterns we see in service calls is a weak front seal while the back seal remains perfect. In almost every case, this is due to an over-adjusted knife. When the knife pressure is too high, it causes the jaws to flex or open slightly after cutting, leading to a poor front seat and incomplete seal. Backing the knife off slightly usually resolves this immediately.
Fix / Prevention:
Verify sealing jaw temperature against film supplier specifications.
Clean sealing jaws frequently to remove buildup or residue.
Adjust sealing pressure and dwell to achieve a uniform bond across the pack width.
Ensure product is centred and not protruding into the seal area.
Check film tracking and tension for stable, consistent feed.
Re-check knife adjustment if the front seal is weaker than the back.
7. Cutting Issues
Symptom:
Packs are not being cut cleanly, partially uncut product. In some cases, the machine may jam as the knife catches the film or jaws.
Likely Causes:
Blunt or damaged cutting knife.
Knife over-adjusted and contacting the jaw face.
Build-up on the knife or residue on the sealing jaw.
Typical Root Cause:
Cutting issues almost always come down to knife condition or poor adjustment.
Incorrect temperature. Sealing jaws expand as they heat up, so does the knife. In some circumstances, a small adjustment to the temperature can cause cutting issues, but in some cases also resolve them.
Fix / Prevention:
Inspect the cutting blade for sharpness or nicks; replace when necessary.
Reset knife depth so it just kisses the anvil or opposing jaw without pressure.
Clean the knife, sealing jaws and surrounding area regularly to prevent buildup.
Confirm jaw timing and knife synchronization after every major service or format change.
8. Temperature Fluctuations
Symptom:
Sealing temperature rises and falls unpredictably during production. Operators may notice the temperature reading oscillating or the seal quality changing between packs — sometimes weak, other times scorched.
Likely Causes:
Faulty or loose thermocouple connection.
Worn or damaged heaters.
Contaminated or oxidised slip rings on rotary jaws.
Typical Root Cause:
Temperature instability is almost always traced back to thermocouple or slip ring issues. A loose or oxidised thermocouple connection will cause the temperature reading to spike or drop erratically, forcing the controller to chase false values. On rotary jaw systems, carbon buildup or product contamination on the slip rings interrupts the heater circuit and creates temporary power loss, especially at high speeds.
Fix / Prevention:
Check thermocouple terminals and tighten or replace connectors.
Clean and maintain slip rings using approved carbon brushes and contact cleaner.
Always replace both the thermocouple and heater together if one has failed — they often degrade as a pair.
9. Film Tension Problems
Symptom:
Film appears loose, bag lengths vary, or print registration drifts during operation. In some cases, the film snaps, wrinkles, or feeds unevenly into the forming box.
Likely Causes:
Unwind brake set too loose or too tight.
Dancer arm travel restricted or incorrectly balanced.
Film roll core slipping on the shaft.
Incorrect roller alignment or dirty guide rollers.
Worn film tension spring/ brake strap.
Typical Root Cause:
Unstable film tension is one of the most common causes of multiple downstream issues — from registration faults to sealing inconsistencies. In most cases, it’s due to poor unwind brake adjustment or a dancer arm not moving freely through its full range. When the film tension fluctuates, the film stretches unpredictably, causing erratic feed lengths and pressure loss at the sealing wheels.
Fix / Prevention:
Adjust unwind brake gradually until film feeds smoothly without jerking or overrun.
Check dancer arm spring tension and pivot movement; lubricate if needed.
Ensure film roll is mounted securely with no slip on the core.
Clean all rollers to remove film dust or residue.
Observe film path at running speed — tension should remain stable with minimal bounce.
If issues persist, inspect tension control sensor or potentiometer for drift.
10. Registration Faults
Symptom:
Printed film drifts off the correct cutting position, causing graphics or logos to appear misaligned on the finished packs. Operators may notice bag length variation or the registration mark constantly “hunting” on the HMI display.
Likely Causes:
Dirty or misaligned registration photo-eye.
Low or unstable film tension.
Incorrect bag length or print pitch parameter settings.
Film slipping on the feed rollers.
Typical Root Cause:
Most registration drift issues are caused by film slippage, poor sensor performance, or inconsistent film control. When the film slips on the feed rollers or tension fluctuates, the print mark physically shifts position between cycles — causing the machine to attempt continuous correction. This constant chasing leads to visible drift in the cut position, even though the photo-eye and encoder may both be working correctly.
Fix / Prevention:
Check and stabilise film tension and feed roller pressure first.
Clean the photo-eye lens and confirm proper alignment to the mark path.
Verify print pitch and bag length parameters in the control system.
Keeping Flow Wrappers Reliable
Most flow wrapper issues trace back to setup, wear, or small alignment errors that compound over time.
Regular checks on film tension, heater condition, forming box alignment, and seal temperature prevent 90% of downtime events before they occur.
At PacMatix, we see these problems daily, across bakery, produce, dairy, and snack applications and our technicians know how to get machines running right the first time.
Whether it’s an urgent breakdown, a recurring seal problem, or preventive maintenance, our team provides expert support backed by genuine experience on GSP and Tecno Pack systems.
Need help diagnosing a fault or improving your line reliability?
KWIK TECH GEMS™
Looking for more real-world fixes and smarter packaging insights?
Visit our growing resource: KWIK TECH GEMS™ — a blog of fast, practical technical tips written by PacMatix engineers for Australian packaging teams.