Whats wrong? My hot water is not working on my Ravenheat rsf 820/20?

Your diverter valve is stuck or jammed. It should move when a hot tap is opened to allow water into the DHW heat exchanger. The valve can probably be cleaned out & re-used. Make sure you let enough water out of the system before dismantling. And remember, the pressurised container holds a fair amount too ! It is a pig of a job to get the valve out, I don't know what kind of tool they use to access the unions when the boiler is assembled. Achilles

Achilles
May 2008

sounds like a faulty flow switch on the dhw not signalling that you opened the tap..

T
May 2008