Sorry but I am too far from you and no time to spare. However, the job is not too difficult:
1. Gas and electricity to boiler off
2. Cold inlet, flow and return service valves off (they may drip/leak through the screws, this is normal for Ravenheat ones)
3. Front, bottom and side panels...
I have recently replaced the diverter valve on a Ravenheat RSF 820/20 (twice). It took just under an hour the first time but don’t make the mistake I made by buying a valve on price alone. An aftermarket diverter from BES, manufactured by Banico, cost around £25 including the micro-switches...