Hi all, same problem with the 24i RSF.
Have had same problem as most above and found remedy of turning off CH and running hot tap full blast until it was running hot water, then turning CH thermostat back on and hot tap off usually did the trick.
However, this morning we've been freezing despote all attempts.
After reading the gas valve banging trick, I wasn't happy to do so with really cold pipes in case of fracture, so tapped a magnetic screwdriver on the valve a few times with mains etc on and hey presto, pilot light flared up!!!
Just though someone may prefer this instead of hammering away at the valve lol
Thanks everyone!!
BERNIE LOGUE
November 2010