Windows 10/117 min readReviewed 2026-07-29

Monitor has horizontal lines until it warms up

Use refresh, cable, source, and OSD comparisons to identify a temperature-sensitive panel fault.

Quick diagnosis

Lines that appear in the monitor OSD with the signal cable removed are generated inside the monitor.

Common symptoms

Horizontal lines are strongest at cold start and fade as the panel warms.
The behavior is repeatable with the same display state.
Changing an unrelated Windows preference does not reliably fix it.

Likely causes

Temperature-sensitive panel timing, driver board, or bonded connection faults can improve temporarily with heat.
A connection, driver, or configuration boundary affecting the display.
Hardware failure only if the symptom follows the same display across controlled comparisons.

Before changing anything

Record the current display settings and connection path.
Change one variable at a time.
Keep a known-good comparison device, port, mode, or application available.

Diagnose it in this order

1
Create a repeatable baseline
Reproduce the symptom in a simple Windows surface and record exactly when it occurs: Horizontal lines are strongest at cold start and fade as the panel warms.
2
Run the discriminating test
Photograph the cold fault, open the monitor OSD with the signal cable removed, and compare a lower refresh plus another source.
3
Apply the narrow fix
Use a lower stable refresh only as a temporary workaround and pursue warranty repair or replacement; do not heat the monitor deliberately.
4
Repeat the original comparison
Keep every unrelated setting fixed and repeat the baseline for longer than the normal failure interval.

Solutions

Monitor has horizontal lines until it warms up

Use a lower stable refresh only as a temporary workaround and pursue warranty repair or replacement; do not heat the monitor deliberately.

Do not open or heat a monitor; internal capacitors and power circuits can retain hazardous energy.

Verify the fix

A replacement or repaired monitor should start cold without lines at its supported mode.
Restart or reconnect once and repeat the same controlled test.
Confirm the change did not create a new failure in the comparison state.

Roll back safely

• Restore the recorded display settings, connection, driver, or mode if the result is not repeatable.

When to stop and escalate

• If the symptom follows the display across another PC or source after the documented checks, use manufacturer support or warranty service.

Related tests and guides

testRefresh rate test

Frequently asked questions

Why test before changing several settings?

A one-variable comparison shows whether the proposed mechanism actually controls the symptom and preserves a safe rollback.

Sources

Troubleshoot external monitor connections in Windows
Microsoft Support. Temperature-sensitive panel timing, driver board, or bonded connection faults can improve temporarily with heat.

Diagnose it in this order

Create a repeatable baseline

Reproduce the symptom in a simple Windows surface and record exactly when it occurs: Horizontal lines are strongest at cold start and fade as the panel warms.

Run the discriminating test

Photograph the cold fault, open the monitor OSD with the signal cable removed, and compare a lower refresh plus another source.

Apply the narrow fix

Use a lower stable refresh only as a temporary workaround and pursue warranty repair or replacement; do not heat the monitor deliberately.

Repeat the original comparison

Keep every unrelated setting fixed and repeat the baseline for longer than the normal failure interval.