Preventing Callbacks: Why Professional Installers Always Stock Multiple Packer Types
Why Callbacks Cost Installation Firms Money
Callbacks are one of the biggest hidden expenses for installation firms.
Every time a team has to return to a property to fix:
- A dropped window
- A rubbing door
- A misaligned lock
- A bowed frame
- A rattling glazed unit
you lose money.
You pay for fuel, labour, time, and sometimes replacement parts — all for a job that was already “completed.”
In most cases, callbacks are not caused by hardware failure or frame defects.
They are caused by incorrect packing.
Professional installers prevent these issues by carrying a full range of packer types and thicknesses so every window and door is installed correctly the first time.
Most Callbacks Are Caused by Poor or Improvised Packing
When installers don’t have the right packers, they often:
- Under-pack
- Over-pack
- Use the wrong thickness
- Improvise with wood or cardboard
- Skip toe-and-heeling
- Avoid using bridge packers where screw heads exist
- Ignore uneven or twisted openings
Every one of these shortcuts leads to problems weeks or months later.
Stocking the correct packers is the simplest way to eliminate these issues.
The Four Types of Packers Every Professional Should Carry
To avoid callbacks, installers must carry more than just flat packers.
Different problems require different solutions.
Flat Packers (Most Common Use)
Used for:
- Toe-and-heel
- Weight support
- Levelling frames
- General spacing
Lack of the correct flat packer size is one of the top causes of misalignment.
Bridge Packers (Prevent Glass Stress and Cracking)
Used when screws or fixings sit under the glazing.
If a flat packer presses onto a screw head, it creates:
- Stress points
- Cracked units
- Rattling glass
- Callbacks
Bridge packers solve this instantly.
Wedge Packers (Correct Uneven Openings)
Used for:
- Out-of-square sills
- Older brickwork
- Fine adjustments
- Precision levelling
Not carrying wedge packers leads to:
- Frames twisted into shape
- Uneven pressure
- Bowing over time
Large Packers (8–12 mm)
Used for doors, heavy frames, and big sashes.
Without them, installers are forced to stack too many small packers — a common cause of movement and instability.
How Incorrect Packing Causes Common Callback Problems
Dropped Windows
Caused by:
- No toe-and-heel
- Wrong thickness packer
- Under-packed hinge side
Correct packers prevent dropping entirely.
Doors Rubbing or Catching
Often solved by:
- Adding a 3 mm, 4 mm, or 5 mm packer
- Using wedge packers for fine levelling
If installers don’t have these sizes on hand, the door won’t stay aligned.
Bowed Frames
Caused by:
- Over-packing
- Packing in the wrong places
- Using improvised shims
Proper packers maintain the frame’s shape.
Cracked or Noisy Glazed Units
Usually caused by:
- Flat packers pressing on screws
- Poor side support
- Under-packed top corners
Bridge packers eliminate this problem.
Draughts or Water Leaks
Often due to:
- Inconsistent spacing
- Blocked drainage paths
- Incorrect packer type
The right packer keeps drainage channels clear.
Why Multiple Packer Types Reduce Labour Costs
When installers carry only flat packers, they cannot deal with:
- Uneven surfaces
- Screw heads
- Large gaps
- Heavy sashes
- Precision adjustments
This forces them to improvise, leading to improper installation and expensive returns.
Stocking multiple types means:
- Faster installs
- Fewer mistakes
- No site delays
- No shortcuts
- No time wasted searching for “something to use as a shim”
This directly reduces labour hours and increases profit.
Procurement Strategy: Stock the Right Quantities
To fully prevent callbacks, installation firms should stock:
Bulk sizes:
- 3 mm
- 4 mm
- 5 mm
These handle most of the work.
Smaller quantities of:
- 1 mm
- 2 mm
- 6 mm
For fine adjustments.
Essential specialist packs:
- Bridge packers (5 mm, 6 mm)
- Wedge packers (various tapers)
- Large packers (8–12 mm)
General flexibility:
- 2–3 mixed sets per van
Buying in bulk ensures every installer has the right packer on every job.
Standardising Packer Usage Across the Team
To fully eliminate callbacks, installation companies should implement:
- A standard packer selection guide
- Clear toe-and-heel training
- Consistent packer placement rules
- No improvised materials policy
- Centralised van stocking decisions
- Regular inspections of packer usage
Consistency is key — not just having the correct packers, but using them the same way across the entire team.
Final Thoughts
Most callback problems in window and door installation are completely preventable.
When installers carry multiple packer types — and know when to use each one — installations remain stable, aligned, and trouble-free for years.
To reduce callbacks, installation firms should equip every van with:
- Bulk flat packers (3, 4, 5 mm)
- Bridge packers for screw clearances
- Wedge packers for uneven surfaces
- Large packers for heavy frames
- Mixed sets for unusual gaps