Dryer Runs No Heat vs No Tumble Decision Tree

Why this matters

The two dryer complaints "runs but does not heat" and "powers on but does not tumble" share a starting symptom (motor energized, no useful output) and split into completely different repair paths within the first five minutes of diagnosis. Mixing them up is the most common rookie failure on a dryer call and costs an unnecessary belt or heating element. The split is binary - if you cannot hear and feel the drum rotating, it is no-tumble. If the drum turns and the air is room temperature, it is no-heat. Once you separate the two, each path is short and high-confidence.

Symptom presentation

Customer says "dryer won't dry." Probe: does the drum turn? If the answer is no, classify as no-tumble. If yes, classify as no-heat. Ask whether the failure is sudden or gradual - gradual heat loss with full tumble points to airflow restriction (lint, vent, blower), sudden no-heat points to a discrete electrical component, and any no-tumble fault is by definition sudden because there is no in-between for a belt or motor.

For electric dryers in the U.S., the supply is 240 V split-phase. Half of that 240 V drives the heating element; the other half plus a 120 V leg drives the motor and controls. The dryer can run motor-only on one hot leg if the other has lost continuity - which is the textbook "runs but no heat" mode caused by a tripped breaker on one pole, a broken house circuit conductor, or an internal thermal fuse open.

Quick checks (under 10 minutes)

• Voltage at the dryer outlet, both hot legs to neutral. 120 V on both is correct. 120 V on one and 0 V on the other = half-tripped breaker or open house wiring; investigate the panel first, not the dryer.
• Lint screen and lint trap housing. Pull and inspect. A clogged screen does not cause no-heat outright but combined with a marginal thermal limit it trips the high-limit and prevents heat - very common gradual presentation.
• Vent run from the dryer to the wall cap. Disconnect at the dryer and run a heat cycle. Heat returns with the vent disconnected = vent is clogged or crushed. Per IRC M1502.4.4 the maximum vent length is 35 feet less 5 feet per 90-degree elbow unless the manufacturer specifies otherwise.
• Drum belt visible through the lint slot or rear access. Severed belt = no-tumble cause confirmed without further opening.
• Motor hum or silence at start. Hum and no rotation = seized drum, frozen blower wheel, or open motor start winding. Silence = no power to motor, door switch open, or thermal fuse open in the motor circuit.

Isolation tree - No Heat

Branch H1 - Open thermal fuse (~30% of no-heat). One-shot thermal fuse on the blower housing or heater duct trips on overheat and never resets. Common cause: clogged vent. Ohm both terminals - infinite = open, replace, then verify vent before releasing the job or it will trip again within a week.

Branch H2 - Failed heating element (~25%, electric only). Calrod element opens internally. Ohm across the element - typical 8-15 ohms cold. Infinite = element open. Visual inspection often shows a clean break in the resistance coil.

Branch H3 - Failed igniter or gas valve coils (~25%, gas only). Igniter glows then opens but valve does not open = bad gas valve coils. Igniter does not glow at all = open igniter or open thermal/safety fuse upstream. Igniter is silicon carbide, 50-400 ohms cold.

Branch H4 - Failed thermistor or cycling thermostat (~10%). Modern dryers use a thermistor reporting drum temp to the control board. Open thermistor = board logs fault, often allows tumble without heat as a safety mode. Ohm at room temperature; spec varies by OEM but 10-15K ohms is common at 70F.

Branch H5 - Open house circuit hot leg (~5%). 120 V at outlet shows one hot leg dead. Customer reports "no heat for weeks." Reset the breaker fully (off then on) and remeasure. Replace the breaker if it trips on test or shows internal arcing.

Branch H6 - Failed control board (~5%). Everything else passes. Verify with OEM diagnostic mode and replace the board only after ruling out the cheap components.

Isolation tree - No Tumble

Branch T1 - Broken drum belt (~50% of no-tumble). Motor hums and runs, drum is loose to turn by hand. Pull the top panel or front per the OEM service manual and visually confirm. Inspect the idler pulley while the belt is off - a seized idler shreds new belts within a week.

Branch T2 - Failed door switch (~20%). Motor will not start at all. Ohm the door switch with the door closed - should be continuous. Open switch = no motor circuit.

Branch T3 - Open thermal fuse in motor circuit (~10%). Some OEMs route the motor power through the thermal fuse. Trips on overheat and kills both heat and tumble. Ohm the fuse.

Branch T4 - Failed start switch or push-to-start (~10%). Motor will not energize. Bridge the switch terminals momentarily - if the motor starts, switch is bad.

Branch T5 - Seized blower wheel or seized drum bearing (~5%). Motor hums and trips on thermal overload. Rotate by hand with power off - resistance much higher than free-running is the tell. Common with rodent nesting in basement installs.

Branch T6 - Open motor start winding (~5%). Hum without rotation, no mechanical bind. Ohm the start and run windings per the OEM service manual. Open start = motor replacement.

Confirming diagnosis

• Heating element: ohm at element terminals with leads disconnected. Visual break confirms.
• Thermal fuse: ohm cold and verify root cause. If you replace a thermal fuse without fixing the vent or blower restriction, the new fuse opens within days. Always identify the upstream cause before closing the job.
• Igniter/gas valve: observe a heat cycle. Igniter should glow bright orange, gas should ignite within 30 seconds, flame holds for the dry cycle. Glow but no ignition after 60 seconds = gas valve coils. Igniter cycles repeatedly without flame = empty propane tank, closed shutoff, or gas line air-locked after service.
• Belt: visual. Replace idler at the same time on units over 5 years - non-negotiable, the idler is the wear part and a new belt on a worn idler is a one-week callback.
• Door switch: ohm cycle through door open/close cycles. Should switch cleanly.
• Motor: spin by hand, ohm start and run windings, ohm to chassis (should be infinite - leakage to ground = condemned).

Remediation - repair vs replace ROI

References

• NFPA 54 National Fuel Gas Code (gas dryer connection and venting)
• IRC M1502 (clothes dryer exhaust venting requirements)
• UL 2158 Standard for Electric Clothes Dryers
• NEC 422.16 (cord-and-plug dryer connection requirements)
• Whirlpool Service Manual W10110215 (Cabrio platform diagnostic mode and component resistance tables)