Some interlocks prevent the door from opening if the drum is moving. The mechanism that detects this is called a pecker unit and it is located around the motor pulley. It connects to the interlock via a cable assembly. If the pecker unit is broken in the "on" position it may be preventing the interlock opening. Visually check and try to activate the mechanism by hand.
Other interlocks have a secondary locking system which ties in with the pressure switch - the mechanism which detects if there is water present in the drum. If this system is faulty - caused by blockages in the filter, pressure vessel or the thin rubber pipe running to the pressure switch the machine "thinks" its still full of water and wont allow the door to be opened. Take off the top cover, examine the interlock from behind and detach any rubber pipes or cables to try to open it from inside. If all else fails, the interlock itself may be faulty and will have to be broken open. A replacement interlock unit and/or catch will of course be required.
Check out www.2ndwave.co.uk/manual.html
dannyboy, October 2008
