What F3 Means
WHICH MACHINES THIS APPLIES TO: F3 belongs to two Asko dryer families that happen to agree with each other, which is rare enough in this range to be worth saying plainly. It is used on the US T731 and T741, and on the TD73A and TD77A in the TD70 to TD77 range. The Logic and heat-pump machines do not use F3; on those the temperature sensor problem is E1.
US T731 AND T741 - WHAT F3 MEANS: the Use and Care Guide's error-message table reads, in full, "This indicates a thermistor problem. Call a service technician." That is the whole entry. Asko names the part and gives no owner check, which is itself the useful information: there is nothing on this one for an owner to try.
TD73A AND TD77A - WHAT F3 MEANS: the Asko Cylinda after-sales index for the range prints F3 as "Thermistor problem", and its separate "Reasons for problems" section explains the behavior: "This will interrupt the program and produce a flashing F3 on the display. An open circuit can be caused by a broken connection or a failing thermistor. The resistance of a healthy thermistor is between 60 kohm and 40 kohm at 20-30 C."
WHAT THE THERMISTOR ACTUALLY DOES: it is the temperature sensor that tells the control how hot the air in the machine is. The control uses it to decide when to switch the heater on and off. If the sensor circuit goes open, the control has no temperature reading at all, and a dryer with no temperature reading is a dryer that cannot be allowed to keep heating. That is why the program is interrupted rather than continued at reduced performance.
A RELATED FAULT WORTH KNOWING ABOUT: the same document describes a thermistor that is electrically sound but has lost thermal contact with the fan casing. It reads: "The heating element will be energized as long as the thermistor does not sense the air temperature called for by the program, resulting in excessive air temperature." That condition does not necessarily show F3, and it is the reason a dryer that runs unusually hot is treated as a service matter rather than as something to keep using.
CLASSIFICATION: problem. The machine stops the program rather than running without temperature feedback.
Common Causes of F3
- Thermistor circuit open, at the sensor or in its wiring
- Connector to the thermistor loose, corroded or displaced
- Thermistor itself failed, reading outside the 40 to 60 kohm band the manual gives for 20 to 30 C
- Thermistor displaced from the fan casing so it is no longer sensing the air it is meant to sense
- Control unit misreading an otherwise sound sensor
🔧 One Safe Check You Can Try
There is no owner repair here and both Asko documents say so in their own way, one by printing "Call a service technician" as the entire remedy and the other by putting the figures in a technician section. What is worth doing is recording the pattern before someone arrives. Note whether F3 appears immediately at the start of a program or part way through, and whether it appears on every program or only on the hot ones - an intermittent problem that appears once the machine has warmed up usually points at a connection that opens as it expands, rather than at the sensor itself. Note also whether the dryer felt unusually hot on the loads before the code appeared. If the machine is going to sit until it is looked at, switch it off at the wall socket or the breaker, and leave it off. Do not remove the back panel to check the sensor or its plug. On these machines the thermistor sits at the fan casing, in the same enclosure as the heating element, its overheat cut-outs and the motor wiring, all of which are at mains potential whenever the dryer is connected, and the resistance figures in the manual are meaningless without the machine isolated and the connector off.
⚠ Why You Shouldn't Go Further Than That
- The thermistor sits in the same enclosure as the heating element and the motor wiring, so the dryer has to be unplugged or switched off at the breaker before the panel comes off, and a built-in or stacked machine has to be freed and drawn out before that panel is reachable at all.
- The heating element and the parts around the fan casing stay hot after a program, so the machine is left to cool before anything is opened.
- The manual quotes a resistance range, not a voltage, which means the reading is only valid with the machine isolated and the connector disconnected; measuring it in place on a live machine gives a wrong answer and is dangerous.
Opening a panel to inspect or repair something yourself doesn't automatically cancel your manufacturer's warranty — but it can risk accidental damage, and some manufacturers do have specific service conditions. Check your product's warranty terms, or ask us, before deciding.