Dryer Thermostat Failure: Too Hot, Too Cold or Cutting Out in Knowle

A dryer usually has more than one thermostat. The cycling thermostat regulates the drum temperature by switching the heater on and off during the cycle. The thermal cut-out is a safety device that opens permanently if things get too hot, and some machines also have a high-limit thermostat or a fuse on the heater. Understanding which one has failed explains the symptom you are experiencing.

Which thermostat does what

The cycling thermostat opens at a set temperature and closes again as the drum cools, producing the sawtooth temperature pattern a dryer needs. If it opens too early, the drum never gets hot enough and drying slows. If it sticks closed, the heater keeps running and the machine overheats. The thermal cut-out does not reset; once it opens, the heater is dead until it is replaced, and the reason it opened needs investigating. A high-limit device protects the heater housing itself.

Symptoms by failure type

Weak or absent heat with everything else working points to a cycling thermostat that opens early or a cut-out that has opened. Overheating, a very hot cabinet, scorched smells or repeated tripping point to a thermostat stuck closed or a heater relay that will not release. Cycles that start well and then lose heat partway through suggest a thermostat drifting as it warms. A machine that will not heat at all after an overheat event usually has an open cut-out.

What we do on the visit

We run the machine and measure the temperature rise across the drum against the expected range, then test the cycling thermostat at its switching points using a controlled heat source rather than a simple continuity check. The thermal cut-out is tested for continuity and replaced if open. We check the heater relay and board output, because a stuck relay produces the same overheating as a stuck thermostat and must be ruled out before a new thermostat is fitted.

Why the cause matters

Fitting a new thermal cut-out without finding out why the old one opened is a common mistake. Restricted airflow from a blocked filter, a clogged condenser or a crushed vent is the usual reason, and a thermostat stuck closed is another. If either remains, the new cut-out will fail the same way. We clear the underlying cause first, then replace the protective part.

Parts and cost

Thermostats and cut-outs are inexpensive and widely available, though older models can be harder to source. The repair is usually quick once access is gained, which varies between machines. If the board or relay is at fault, that changes the cost significantly, and we will tell you before ordering. Parts are quoted separately from labour.

Safety

Never bypass a thermostat or cut-out, never fit a fuse of a higher rating, and never run a dryer that has overheated. A machine that has overheated may have damaged wiring or a distorted heater housing that is not visible from outside. If there is a burning smell, stop using it; if there is smoke or flame, leave and call 999.

After the repair

Run a normal load and check that the machine heats, completes the cycle and does not become unusually hot. Feel the cabinet after twenty minutes; it should be warm, not uncomfortable. Keep the filter clean and have the vent checked, since those are the two things most likely to stress the thermal protection again.

Booking

Tell us whether the dryer is not heating, overheating or cutting out, and whether it has ever tripped a thermal cut-out. Give the brand, model and dryer type. If the machine has overheated, mention it, because we will want to inspect for secondary damage as well as test the thermostats.