What can be the fault in whirlpool washing machine which is causing wide voltage fluctuation whenever plugged to main supply

It appears your circuit is not robust enough to power your washing machine.

Well if the alarm is going off then there is a problem, get it taken car of asap before you ruin a fridge and freezer full of expensive food.

unplug the set wait an hour then with a magnfying glass look at all your "can" capacitors on your powerboard if any of them are rounded on top have pinholes on the top they are bad replace them capacitors charge then discharge power if they are only working partly as a group you will have voltage fluxuations and not enough power to turn the set on

Fiats have a reputation for electrical/electronic problems as they age and even when they are not very old they can manage strange things that even sometimes defeat the dealers, though the same can be said of many modern vehicles. I used to look after a Ducato motorhome and fortunately didn't need to get involved with much electrical work - the only faults were caused by the coachbuilders rushing around and being careless and not by Fiat.

I am not sure if the temp gauge is driven by the engine management or is a traditional circuit but either way the temperature gauge is in effect a voltmeter of sorts. Assuming the gauge is ok, the reading will only fluctuate if the voltage in the circuit fluctuates and that could mean the supply voltage is fluctuating or the resistance of the ground path is fluctuating.

With the traditional circuit the gauge is supplied by an electronically stabilised voltage and the ground path resistance is varied by the engine coolant temperature sensor and fluctuations could be anything from a faulty instrument voltage regulator, through faulty wiring or connections to the temperature actually fluctuating.

If the gauge is driven by the engine management the same approximately applies but checking the circuit becomes much more complex due to the need for circuit diagrams and specialised test equipment, though these would not be needed just to check the security of the gauge in the printed circuit of the instrument panel.

Electric field or an armature problem in the motor maybe here is a manual
Service Manual free download schematics datasheets eeprom bins pcb repair...

The F11 fault code indicates a serial communication error between the Machine Control board and the Motor Control board. This can be caused by several different problems.

A failed Machine Control board could be failing to provide the Motor Control board with proper voltage. If this is causing the F11 code, then the Machine Control board would need to be replaced.

The Machine Control board could also be failing to supply proper voltage to the door lock assembly. The Machine Control board would need to be replaced for this failure as well.

Voltage flows from the Machine Control board to the Door Lock Assembly. The Door Lock then energizes and closes the Door Lock MAIN Switch. Voltage flows out of the Door Lock Main Switch to the Motor Control board. So if you have power into the Door Lock Assembly but not out of the Main Door Lock Switch, it will give you an F11. If so, you will need to replace the Door Lock Assembly.

You could have a bad Motor Control board that is causing this failure. A bad wiring connection between the Motor Control board and the Machine Control board could also cause this fault code. A bad wiring connection between the Motor Control board and the drive motor is also a possible failure. A failed drive motor could also cause the F11.

With so many possible causes for this failure, I recommend calling a service technician to diagnose and repair the problem in your washer. If you are able to unplug the washer and check the wiring connections, you may be able to find a loose wire harness connection that is causing the problem. Much of the diagnosis for the potential problems noted above requires live voltage checks. I do not recommend conducting these types of checks yourself. Unless you want to take a chance and replace the Machine Control board and the Door Lock Assembly,

If there is no power at all to the panel or board then it is possible that there is some damage to the main controller board and circuit. it can be fault within the board, could be the power supply section -DC side - or there is fault in the processor or memory.
In both cases you need to remove the front panel to confirm by measuring the voltage present.

So we just fixed our EWT806 after it suffering the dreaded EF fault... The problem... Too higher mains voltage coming into the house! Albiet within specification from the supplier, the Electrolux EWT806 doesn't like anything around 250 volts! Obviously a poor design on the control board which is unable to accept a wide supply voltage!

Solution, isolation transformer inline with the machine. Now it runs like a dream!

sounds like the drain is blocked. remove the lower front panel from the machine and there you will see next to the pump a drain plug,, unscrew the drain plug counter-clockwise and drain and remove the plug and screen. clean out any socks or whatever else found its way down there. put plug back in and start wash cycle,, all should be good.
if it is still not draining then you could have a bad pump ,, use a volt meter to test for voltage at the pump when it is in drain cycle,, if there is voltage then the pump is bad,, but if there is no voltage then the problem could be at the main control board.

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Phase error does mean low current only a current rectifirer will solve this will keep voltage regulated dipending on the load of machine it could be expensive to buy a proper voltage regulator for it