What F4 Means
WHICH MACHINES THIS APPLIES TO, AND WHY THIS ONE MATTERS MORE THAN MOST: F4 is the code in the Asko dryer range where two families disagree outright. On the US T731 and T741 it reports that the overheat protection device has operated. On the TD73A and TD77A it reports fluff in the filter or the condenser. Those are related conditions - a blocked filter is the usual road to an overheat trip - but they are not the same statement, and a machine that has actually tripped its overheat protection has been hotter than it is allowed to get. Read the section for your own machine.
US T731 AND T741 - WHAT F4 MEANS: the Use and Care Guide's error-message table reads, in full, "This indicates the overheat protection device has activated. Clean the lint filter and try running the program again." So Asko is telling you two things at once: a protective device has done its job, and the first thing to correct is airflow.
TD73A AND TD77A - WHAT F4 MEANS: the Asko Cylinda after-sales index for the range prints F4 as "Fluff in the fluff filter or in the condenser (indicated after end of program)". The parenthesis matters. On these machines F4 is not a mid-cycle stop; it appears once the program has finished, as a report on how the cycle went. The same document ties the indication to a thermostat with an automatic reset that breaks at 115 C, and adds "Not all markets", which is why some machines in the range never show it.
WHAT THE OVERHEAT PROTECTION DEVICE IS: a dryer has a thermostat or cut-out in the hot air path that is not part of the normal control at all. Its only job is to cut the heater if the air gets hotter than the design allows. It operates when air stops moving through the machine, because the heater keeps putting the same energy into air that is no longer carrying it away. The Asko Cylinda document describes exactly this chain for the range: "Filter clogged: The overheating cutout (150 C) will operate, and the machine stops. Must be reset manually."
WHY IT IS TREATED SERIOUSLY HERE: lint is the most flammable thing in a laundry room, and the condition that trips the cut-out is a heater running into stationary air full of it. A machine that trips once, is cleaned and then behaves is a machine that had a blocked filter. A machine that trips repeatedly after the airflow path has been cleaned is reporting something other than lint, and running it to see what happens is not a reasonable test.
CLASSIFICATION: on the US machines, a protective trip. On the TD73A and TD77A, a post-cycle maintenance indication. Both start at the same place, which is the filter.
Common Causes of F4
- Lint filter blocked, or blinded by fabric softener film while still looking clean
- Condenser clogged with lint on a condensing machine
- Exhaust duct crushed, collapsed, packed with lint or blocked at the outside flap on a vented machine
- Dryer installed where it cannot draw enough air, so the air it does draw is already warm
- Overheat cut-out or the thermostat that reports fluff operating early or failed closed
- Heater circuit staying energized because the control has lost its temperature reference
🔧 One Safe Check You Can Try
Switch the dryer off and let it cool completely before you touch anything - the trip happened because the inside of the machine got hotter than it should, and the filter housing and the duct behind it hold that heat. Once it is cool, take the lint filter out and clean it properly rather than quickly: peel the lint off, then wash the mesh under a tap and dry it before refitting, because fabric softener leaves a film that blocks air while the mesh still looks clear. On a condenser machine, clean the condenser as your own manual describes and check the condensate container is empty and seated. On a vented machine, follow the exhaust duct along its whole run and check it for a crushed section, a collapsed flexible length, or lint packed at the wall outlet, and check the outside flap actually opens. Then run a program and watch it. If F4 returns on a machine with a clean filter, a clean condenser or a clear duct, stop using the dryer and have it looked at, because the cut-out is then operating for a reason other than lint. Do not try to find and reset the cut-out yourself: on these machines the manual reset sits inside the cabinet next to the heater, and getting to it means taking a panel off a machine whose heater circuit is live whenever it is plugged in.
⚠ Why You Shouldn't Go Further Than That
- The machine has just been hotter than its normal working range, so it is switched off and left to cool before the filter housing, the duct or anything else is touched.
- The manual reset for the overheating cut-out is inside the cabinet, alongside the heater and its wiring, which are at mains potential whenever the dryer is connected to power.
- Resetting a cut-out without finding out why it operated puts the heater back into the same conditions that made it operate, and the material packed around that heater is lint.
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.