yep, long screwdriver with small philips head is all you need. Thanks to these replies we just completd this job in 15mins. All now working fine and ready to go again if pressure builds up due to (her) not descaling it as part of her weekly chores. Mind you she might blow a valve on reading this ha ha ha
Actually the shower company help line was very good too!
andy from Woodbridge UK, June 2013