THE SHORT ANSWER
If the moving glass section slides down or will not hold its position, stop using it and arrange window service. A support mechanism may need attention, but the symptom does not identify the failed part. Do not prop the sash open or release its tilt hardware to investigate.
Before you try anything
Keep hands and other people out of the sash path. Keep children away from the opening; an insect screen cannot prevent a fall. Work only from the floor and do not lean through the window. Do not remove sash, jamb liners, cords, springs or balances. Preserve existing safety devices and required emergency escape access.
Before you begin
For an existing single- or double-hung window with a vertically moving sash. This is a safe reporting guide, not a balance-reset or replacement procedure. Casement windows, horizontal sliders and patio doors have different mechanisms.
A photograph taken from a safe position, the window brand or product label if already accessible, and notes about when the movement changed. Do not reopen the window to find a hidden label.
In a rental, report the problem to your landlord or property manager before making repairs. Building rules and local requirements vary.
Work through the checks
- 01
Stop repeating the movement
If the sash has already slipped, do not release it again to see how quickly it falls. Keep the area clear.
- 02
Leave it in a safe condition
If already closed, leave it closed and use the ordinary lock only if it engages normally. If open or unstable and you cannot close it safely, keep people clear and request prompt assistance.
- 03
Identify the window type from existing information
Single-hung windows have a moving lower sash; double-hung models can have two moving sashes. Do not assume an unfamiliar upper sash should move.
- 04
Record the history
Note whether the problem began after cleaning, tilting or another change. Describe any uneven position or sound already observed, without repeating the action for a recording.
- 05
Contact the manufacturer or property manager
Provide the existing photos and model information. Ask for qualified service rather than ordering a balance from the symptom alone.
What your result means
These observations help choose a next step. They do not confirm a diagnosis.
| What you notice | What it tells you | Next step |
|---|---|---|
| Problem began after tilt cleaning | The cleaning history matters | Tell service staff; do not repeat a model-specific reset from another window. |
| One side looks lower | Alignment needs assessment | Keep clear and avoid lifting one corner to correct it. |
| Closed sash locks normally | It can remain out of use pending service | Do not reopen it to test support. |
| Open sash cannot be safely controlled | There is an immediate handling concern | Restrict access and obtain prompt help. |
Know what happens next
Check the outcome
Have the service provider explain the repair and demonstrate documented normal operation. A prop, a lock holding a closed window, or one successful opening does not establish that the support mechanism is sound.
When to call a professional
Stop at the first uncontrolled movement, loose or damaged sash, broken glass or inaccessible work area. An opening used for emergency escape requires prompt attention to continued safe access; do not permanently block it as a repair.
Take useful notes with you
A short record makes it easier to explain the problem to a landlord, technician, or responder. Do not collect notes during an emergency.
Notes stay in this page until you leave or reload. Download a copy to keep them. They are not sent to us.
Common questions
Does sliding down prove a broken balance?
No. Model-specific support or engagement needs assessment.
Can I use a stick to hold it open?
Do not use a makeshift prop as a repair.
Will the screen protect children?
No. CPSC warns against relying on insect screens to prevent falls.
Sources & scope
This is a desk-researched guide, not a hands-on test or an on-site diagnosis. A licensed tradesperson has not independently reviewed this edition. Follow your product’s manual and local requirements.
- Andersen — Resetting Balancers on A-Series and 400 Series Tilt-Wash Windows
Supports model-specific balancer engagement after tilt cleaning and professional help. Its reset requires sash handling; no reset steps are reproduced or generalized.
- Andersen — Single-Hung vs. Double-Hung Windows
Supports the distinction between moving lower sash and two moving sashes. Product features are not generalized to every brand.
- CPSC — Preventing Window Falls
Supports keeping children away from openings, not relying on screens, and preserving escape considerations. It does not diagnose or repair sash mechanisms.
Published 2026-10-07 · Our editorial policy · Report a correction