Hotpoint Aquarius DWM55?

Most probably a defective heating element.

You can do some diagnosis by working out just when in the machine's cycle the trip trips.

Water is let in (inlet solenoid)
It gets sloshed around (circulating pump)
It gets heated (heating element)
The detergent flap operates (detergent solenoid)
The drain pump operates (drain pump)

i.e when does it trip?

Peccavi
March 2010