Indesit WI 121 keeps filling

Last week my washing machine started sticking on all programmes. After reading previous messages i was led to believe it could be the heater element so i swapped the hot and cold inlets over to increase the water temperature. This enabled the machine to complete the cycle.

Then once it had drained and the cycle finished it refilled up! After watching a complete cycle there are points when the machine stops water flow into the machine (which leads me to believe its not the inlet valve) Even after replacing the hot and cold onto there correct inlet positions and forcing the machine onto a drain cycle it continues to refill!

I have a heater element on order but don't understand why the machine refills any help would be appreciated.

If it's continually filling does it not flood?
If not check the drain hose isn't syphoning.
Make sure it's not too far down the stand pipe and that the drain hose lifts as high as the cable entry on the rear of the machine.

After it refills, it then drains while filling, leaving the water level constant (ie washer full). Water enters the machine via the soap tray so its not coming back from the drain.

The machine programme light flashes as if the wash programme has finished, so i don't understand what is still powering the inlet valve and drain valve to stay open!

If it's syphoning you'll get exactly what you describe. Is the waste pipe into a stand pipe? or a spigot under the sink?
As to the light flashing, count the flashes between pauses and post the result here.

The drain goes into a waste pipe and straight out the wall into a drain. As was the case when it was working. I have checked that the drain hose is at the correct height after coming out of the machine.
Once the wash cycle finishes there is one flash per pause, which is what it did when it worked to indicate that the programme had finished!
Thanks for your input with this.

Very strange fault.
If a new heater doesn't cure it (be sure to check for internal breakage of the wires to the heater, they look ok but break inside the insulation) then I suspect we're looking at a pcb fault.