An Indesit washing machine producing error F04 is producing an error code that means, “pressure switch jammed on empty – check pressure switch and module”. (or if fitted with a rotary dial that clicks round and round accompanied by 4 cyclical flashes of the LED).
The pressure switch works on air pressure and lets the main programmer (or PCB) know when the washing machine has water inside. By default it’s indicating “empty” when no water is in the washing machine. As water enters the machine, air pressure is forced up a rubber or plastic tube and eventually clicks the pressure switch over whereupon the programmer knows the correct level has been reached.
This error code appears to say the main pcb module is not receiving a message that the water level has risen inside the washing machine despite it letting in water. It could mean a faulty pressure switch, but it could also mean the pressure switch is OK but the pcb module has got a fault or there’s a connection problem between them. The most common cause of a fault in the pressure system is a simple blockage (Faults on pressure system).
In theory it could be that no water has entered the washing machine in the first place which would also never trigger the pressure switch. However, there’s a special H20 error code to indicate not filling. I’m presuming maybe the F04 error might mean the pressure switch has moved away from empty but not clicked up to register the level of water
Some Hotpoint washing machines also share the same error F04 description although the advice there is to check the pressure switch and “wiring and module connections”.