I need to replace my Gainsborough 2000 7.5 KW shower as the solenoid has gone and it makes a funny buzzing noise producing hardly any heat or flow. The switch in the cupboard is jammed on and I can't turn it off to isolate it before changing. How can I fix this ? Also, I need advice on buying a new shower to replace this one. There are Tritons and Galaxy that seem to come out in the searches. I don't want to pay much more than £50-80 if I can help it. Any recommendations will be appreciated. Thanks.