Intermittent heating in a clothes dryer can come from airflow problems, temperature‑safety devices, heating components, electrical supply issues (electric dryers), or ignition parts (gas dryers). [6][7]
Before you open or test anything: disconnect power for electric dryers (unplug or shut off the breaker) and shut off the gas supply for gas dryers; also ensure a working carbon monoxide alarm is installed when a gas dryer is present. [1][6]
If you smell burning, see smoke, or detect a fire, stop the dryer immediately, disconnect power or shut off gas, and call emergency services—lint buildup is a common ignition source. [1][2]
Start with lint and airflow (most common, and safety‑critical)
Lint buildup inside the dryer or in the exhaust duct is a major contributing factor in dryer fires; the CPSC warns that lint accumulation can cause fires and provides guidance on overheated dryers. [1]
Routine lint‑trap cleaning after every load and a scheduled annual inspection and cleaning of the dryer exhaust duct materially reduce fire risk; inspect the duct sooner if drying times increase. [1][3]
Check exterior vent performance while the dryer runs: weak exterior airflow indicates a vent or duct restriction that should be cleaned or shortened before replacing heating components. [3][6]
Do not use flexible foil or plastic ducting for permanent runs—DOE and manufacturer guidance discourage or prohibit these materials because they trap lint and restrict airflow. [3][5]
Dryer exhaust ducts must terminate outdoors and must not discharge into attics, crawlspaces, or garages; manufacturer instructions and codes set material and termination requirements, and a damper or flap that opens with airflow is required at the termination. [4][3][5]
Airflow and vent length: what to check
Manufacturers publish model‑specific vent‑length tables that reduce allowable equivalent length for each elbow and depend on duct type and hood style—follow the specific model manual for exact allowable equivalent length. [5]
Common maximum vent lengths quoted in examples vary (for instance 25 ft or 35 ft) because manufacturers and codes differ; always follow the dryer manufacturer's installation instructions first, then local code if the manufacturer is silent. [4][5]
Diagnosing component failures: electric dryers
When the drum spins but there is no heat, common causes include a blown thermal fuse/thermal cutoff (a one‑time device that must be replaced), a failing heating element, a faulty cycling or high‑limit thermostat, control/timer faults, or a lost/damaged 240 V leg. [6][7]
Use a multimeter to test fuses and thermostats for continuity; an open thermal fuse must be replaced with the correct OEM part because it is not resettable. [7]
Measure outlet voltage to check for a lost 240 V leg—an intermittent or missing hot leg can cause intermittent heating. If you need to change or add a 240 V circuit, see guidance on dedicated dryer circuits before attempting electrical work. [6][7]adding a dedicated 240V circuit
Diagnosing component failures: gas dryers
Gas dryer intermittent heating commonly stems from a weak or failing igniter, malfunctioning gas valve coils (solenoids), flame sensor issues, or tripped thermal cutouts. [6][7]
Observe the ignition sequence—glow of the igniter, opening of the gas valve, then flame—to help isolate whether the igniter, gas valve coils, or flame sensor is failing. [6]
Always shut off the gas before testing components and, after repairs, verify there are no leaks before re‑pressurizing the line. If you are not comfortable working on gas appliances, hire a qualified appliance technician. [6][1]
Stepwise diagnostic checklist
Safety: unplug or trip breaker (electric) or shut the gas supply (gas) and confirm CO alarm present if gas. [1][6]
Check lint trap and drum interior for lint or obstructions; clean lint trap each cycle. [1]
Run the dryer and check exterior vent airflow; weak flow means clean or shorten the duct before replacing parts. [3][6]
Inspect duct type and routing: replace flexible foil/plastic with rigid or semi‑rigid metal and minimize elbows/length per manufacturer instructions. [3][5]
Electric: if drum spins but no heat, measure outlet voltage for both hot legs and test thermal fuse and thermostats for continuity with a multimeter; replace open thermal fuses with the correct OEM part. [6][7]
Gas: observe ignition cycle to isolate igniter, gas valve coils, or flame sensor; replace failing ignition components following manufacturer guidance. [6][7]
If you lack experience with electrical testing or gas appliance service, hire a qualified appliance technician. [1][6][7]
Costs and parts
Typical part price ranges from parts suppliers: thermal fuses commonly cost roughly $10–$40; heating‑element assemblies commonly range from about $30–$150+; gas igniters or gas valve coils commonly range approximately $20–$150+ depending on model. Labor and service calls add to totals. [10][7]
Consumer price guides report typical professional dryer repair service‑call and repair totals commonly span roughly $100–$430 for common repairs, with many commonly quoted averages around $150–$200; gas dryer repairs may trend higher due to ignition and gas‑part complexity. [8][9]
Final safety reminders
Follow the dryer manufacturer's installation and repair instructions for model‑specific requirements, vent lengths, and approved materials—manufacturer instructions govern for that model. [5]
Never terminate dryer exhaust indoors; keep vents clear, test for leaks after any gas repair, and call emergency services for active fires. [4][1]
Resources and how to get help
CPSC guidance on overheated dryers and lint hazards. [1]
DOE dryer venting job aid for recommended materials and cleaning intervals. [3]
Manufacturer troubleshooting and installation instructions for model‑specific diagnostics and vent‑length tables. [5][6]
Repair guides and parts suppliers for replacement components and multimeter testing procedures. [7][10]