Here is a symptom that confuses a lot of people: the dryer gets properly hot on high heat but blows cool air on low or medium. Or the reverse, where delicate cycles feel warm and the regular cycle stays cold. Because some heat is getting through, it is tempting to assume the dryer is fine and just slow. It is not, but this pattern is actually helpful. It narrows the problem to the handful of parts that decide how much heat each setting gets.
We get this call regularly in Calgary, and it is almost always a parts-testing job rather than a guessing game. Here is how heat settings work, what each pattern usually means, and what you can check before booking a visit.
How dryers make different heat levels
A dryer does not have a dimmer for heat. It switches the heat source fully on and fully off, and on some models it also changes how much of the heat source is used. Depending on the model, it does this with:
- A cycling thermostat with a small built-in heater, often called a bias heater, that warms the thermostat so it cycles off sooner on low and medium.
- A thermistor and electronic control that read the air temperature and switch heater relays on and off to hit a target.
- A heating element with two coils on some electric models, where both coils run on high and only one runs on lower settings.
- The timer or temperature selector switch, which routes power to different circuits for each setting.
When one of these fails, one setting stops working while another carries on, which is exactly the symptom you are seeing.
It also helps to know that high heat on most dryers is not so much hotter heat as heat that stays on longer before cycling off. Low and medium simply let the drum cool sooner between bursts. That is why a weak part on a lower circuit can go unnoticed for months: the clothes still dry, just more slowly, until one day the setting produces nothing at all.
Heats on high, not on low or medium
Cycling thermostat or bias heater
On many older and mid-range dryers, the low and medium settings send power through the bias heater inside the cycling thermostat. If that tiny heater burns out, or the thermostat has weakened, the lower settings may barely warm up or cut out after a few minutes. High heat does not use the bias heater, so it keeps working normally.
Temperature selector switch
The switch or knob that picks the heat level can wear out or burn its contacts over time. When one position fails, that setting gets no heat at all, while the others are unaffected. A selector that feels loose or crunchy when you turn it is a hint. On electronic dryers the control board does this job, so a dead setting there usually means a relay or the board itself rather than a separate switch.
One coil of a dual-coil element
On dryers with a two-coil element, if the coil used on lower settings breaks, low and medium go cold while high still warms up on the remaining coil. Clothes will dry on high, but slower than they used to. See our post on signs of a failed heating element for the other clues.
Heats on low, not on high
The safety system stepping in
This pattern often means the dryer is protecting itself. On high, a dryer with poor airflow reaches the high-limit temperature quickly and shuts the heat off, then cycles on and off so fast that the drum never feels properly warm. Gentler settings never get hot enough to trip anything. So "only works on low" is often a vent problem in disguise. Our post on a dryer that runs too hot explains how this happens.
Clues that point to airflow include clothes that take two cycles to dry, a laundry room that feels warm and humid, and a cabinet top that is hot to the touch. If you notice these, have the vent checked before replacing any heat parts, or the new part will be working against the same restriction.
A failed coil, relay or timer contact
If airflow is strong, the cause may be the opposite coil on a dual-coil element, a heater relay on the control board, or a worn contact inside the timer that only feeds the high-heat circuit.
Gas dryers and electronic controls
Gas models
Gas dryers usually have a single burner that is either on or off, so a setting-specific fault on a gas model normally points to the thermostat, the selector switch or the control rather than the burner. If the dryer heats on one load and not the next, that is a different pattern, often linked to gas valve coils, and our gas dryer repair page explains it.
Sensor cycles and fault codes
On newer dryers, the control decides when to add heat using thermistor readings and the moisture sensor. A faulty thermistor or relay can make one cycle heat and another not. Some models log a code: on Whirlpool-built dryers F4 E1 is a heater system fault, Frigidaire's E5B means the temperature is not rising, and Electrolux uses E61 for a heater relay failure. Look up your brand on our dryer error codes page. Make sure the moisture sensor bars are clean too, because a dirty sensor ends cycles early and can look like a heat problem. See how to clean a dryer moisture sensor.
Which part is likely?
| Pattern | Likely cause | Who fixes it |
|---|---|---|
| Hot on high, cool on low and medium | Bias heater or cycling thermostat | Technician |
| One setting has no heat at all | Selector switch | Technician |
| High is warm but slow, low is cold | One coil of a dual-coil element | Technician |
| Low works, high feels lukewarm | Restricted vent tripping the high limit | DIY vent check first |
| Sensor cycles cold, timed dry warm | Thermistor, relay or dirty sensor bars | DIY sensor clean, then technician |
| Eco or delicate cycle feels cool | Normal lower-heat setting | No repair needed |
Safe checks before you call
Unplug the dryer or switch off its breaker before touching anything, except while running the test cycles in step one.
- Run each heat setting on a timed dry for about ten minutes and note which ones get warm. Write the results down; they speed up the diagnosis.
- Clean the lint screen and check for a strong, steady airflow at the outside hood.
- On electric dryers, switch the double breaker fully off and then firmly back on.
- Check that you are not using an air-only, wrinkle-prevent or eco setting that limits heat by design. Your manual lists which cycles run cooler.
- With the dryer unplugged, wipe the moisture sensor bars with a little rubbing alcohol.
Do not open the control panel or jump a thermostat to see whether it heats. That can overheat the dryer, blow the thermal fuse and damage the control board. On gas models, leave the burner and valve alone, and if you ever notice a gas smell, get out of the house and phone ATCO Gas emergency at 1-800-511-3447.
When to call a technician
Partial heat means testing thermostats, coils, the selector switch, the timer or the control relays with a meter, then replacing only the part that has failed. Fast Appliance Repair diagnoses dryer heating problems across Calgary and in Chestermere, Okotoks, Airdrie and nearby towns, on both gas and electric dryers. Call (587) 779-6919 for same-day service. We charge a flat diagnostic fee, quote the full job before starting, and cover the repair with a 90-day parts and labour warranty.