Kenmore Dryer F28: Moisture Sensor Signal Lost
What Your Dryer Is Telling You
Error F28 on a Whirlpool-built Kenmore dryer (model prefix 110.xxxxx) means the moisture sensing system cannot obtain valid readings from the sensor bars inside the drum. During auto-dry cycles, two metal bars mounted on the inside of the drum front panel detect remaining moisture by measuring electrical conductivity between them through tumbling clothes. F28 posts when the board receives no signal variation during the sensing window — the bars appear electrically inactive.
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Check Your Model Prefix
This code applies to 110-series (Whirlpool-built) Kenmore dryers. Model prefix 796 (LG) or 417 (Frigidaire) = different manufacturer, different codes.
The Moisture Sensing System
Two curved metal strips are visible inside the drum front — usually near the lint screen housing. As damp clothes tumble and contact both bars simultaneously, a tiny current flows through the moisture in the fabric. The board measures this current to gauge drying progress. Dry fabric conducts poorly; wet fabric conducts well. As the load dries, conductivity drops until the board determines the clothes are dry enough and ends the cycle.
Safety First — Know the Risks
Gas dryers carry carbon monoxide and explosion risk. Even electric dryers involve 240V circuits that can deliver a fatal shock. Our techs are licensed and insured — let them handle the risk.
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Dryer Sheet Film: The #1 F28 Cause
Fabric softener dryer sheets deposit an invisible waxy film on the sensor bars over hundreds of loads. This film is electrically insulating — it prevents the bars from making conductive contact with damp fabric. The bars look perfectly clean to the eye but are coated in a layer that blocks the moisture signal completely.
Fix: Scrub both bars with rubbing alcohol and a non-scratch scrubbing pad (like a green Scotch-Brite pad). The waxy film dissolves quickly. Dry the bars and run a test load on auto-dry. This 2-minute cleaning resolves F28 in approximately 50% of all cases.
Prevention: Switch to liquid fabric softener (added in the washer) or wool dryer balls. If you must use dryer sheets, clean the sensor bars monthly with alcohol.
Bar Surface Oxidation
Over years, the metal bars develop surface oxidation that reduces their ability to conduct through damp fabric. Light oxidation is invisible; heavier oxidation shows as a dull, slightly discolored surface. Scrub with fine sandpaper (220 grit) followed by alcohol cleaning to restore bare metal conductivity.
The Real Cost of DIY
Average DIY attempt: $150-400 in tools you may use once, plus the risk of further damage. Our diagnostic visit costs $0 — we find the problem and give you an honest quote.
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Wiring From Bars to Board
The two sensor bars connect to the main board via thin wires routed through the drum front panel and the dryer cabinet. These wires can break at their solder points on the bars, at connector pins where the harness plugs into the board, or where they pass through the cabinet structure.
Test: Measure continuity from each bar to its corresponding pin at the board connector. Each path should read near-zero ohms (under 2 ohms). Higher resistance or open circuit indicates a wire break or corroded connector.
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Board Sensing Circuit
The board's moisture sensing ADC can fail — unable to measure the tiny current between the bars even when bars and wiring are fully functional. This is an uncommon cause of F28. Board replacement: $80-$180.
Don't Void Your Warranty
Opening your appliance yourself may void the manufacturer warranty. Our repair comes with a 90-day guarantee, and we document everything for warranty compliance.
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Timed-Dry Workaround
F28 only affects auto-dry cycles — the cycles that rely on moisture sensor feedback to determine when to stop. Timed-dry cycles run for a fixed duration regardless of moisture level and do not use the sensor bars at all.
If F28 is preventing you from drying clothes, switch to a timed-dry cycle as a temporary workaround. Set the timer based on your experience with the load type — typically 40-60 minutes for a normal mixed load on medium heat.
Cost Summary
| Cause | Parts | Professional Repair |
|---|---|---|
| Dryer sheet film cleaning | $0 | $90-$130 |
| Bar oxidation cleaning | $0 | $90-$130 |
| Wire/connector repair | $0-$10 | $120-$180 |
| Control board | $80-$180 | $200-$350 |
Is It Worth Your Time?
A dryer not heating could be the element, thermal fuse, gas valve, igniter, or timer. Average DIY diagnosis: 3-4 hours with no guarantee of finding the issue. Our technician diagnoses the issue in about 30 minutes — same-day appointments available.
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Questions About Kenmore F28
F28 only shows on auto-dry. Can I just use timed-dry? Yes — timed-dry does not use the moisture sensor. This is a valid workaround. However, auto-dry is more energy-efficient because it stops when clothes are actually dry rather than running a fixed time.
How do I know if the bars are coated vs. genuinely failed? Clean the bars with alcohol first. If F28 clears after cleaning, the coating was the issue. If F28 persists, test wiring continuity from bars to board.
F28 and clothes come out still damp on auto-dry. Related? Yes — without valid sensor readings, the board cannot determine when clothes are dry. It may end the cycle prematurely by defaulting to a "dry" assumption when no moisture is detected.
F28 persisting after sensor bar cleaning? Our technicians test the full sensing circuit path from bars through harness to board. Book your diagnostic.
