Thanks OnePlan ! I thought I'd read every online manual but missed this one... I don't think the "uninstallers" didn't read it either as they didn't drain it while still connected. We weren't planning to connect it until we put the kitchen in later this year (the quooker can as part of an ex display eBay bargain) but maybe we should bring that forward (I'm sure DH would like that - kitchen toys !)
I assume a competent electrician can install this - we don't need to get quooker to reinstall ?