Bosch WAQ28461GB_WH - Power goes during cycle

I would try to use a temporary extension lead as long as the extension cable definitely has an earth. If it is a 13 amp extension lead they should be earthed. It's definitely possible the socket could be at fault. I recently got caught out with one when my own microwave started cutting out and struggling to run. I took it in to my local repairer who couldn't find any fault so I examined my wall socket and found an extremely loose connection in there along with some burning. I replaced the wall socket with a new one.

If they send and engineer and find the wall socket faulty then they will charge as it isn't a fault with the washing machine. However, if it isn't a fault on the wall socket, but a genuine intermittent fault on the washer and they don't find anything (particularly if they don't spend much time looking for the fault) then they shouldn't really charge. They might say there's no evidence that there is a fault but I would say there is equally no evidence that there isn't a fault. It's a difficult situation, and they must get a lot of people calling them out on a whim, but if you know you have a fault I would refuse to pay just because they can't find it - read my article here - Repair company want to charge if engineer can’t find fault