Would be grateful of any advice. Eight year old Vokera Excell 80. Generally has been great (serviced three times in all) though hot water problems last couple of years; diaphraghm replaced. Since around then also pressure dropping slowly (now guessing a leak somewhere) - well into red but heating still always working. Engineer cancelled on me week before Christmas, I hoped to get through the festive period ok. Unfortunately the heating has now stopped as of 2 days ago, pressure finally at 0. Was able last night to top up from filler loop after searching on net. Now at 2 (higher than I meant but it ran away a wee bit - that was scary!). Can't get heating back on though. Have tried setting all bits off (not pilot, it's fine, haven't touched it) then resetting its electricity supply. It whirrs, it reacts more when I switch the timer to constant but there's still no heating. Can it have locked itself out somehow after the low pressure? Is there a simple thing I can do myself to have heating within the next week? Thanks.