No hot water or central heating at all - gas

Hi all
Last night my I came home to find my whole central heating system up the spout (pardon the pun). There appears to be no power at all to the system (I'm assuming this because the clock is running on it's battery). When I checked the fuse box i found that there was no spearate fuse for the system and all the other fuses were fine. I have also checked the gas supply and is connected too. When I tried to use the immersion heater, the light came on, but this also failed to heat the water....any suggestions on where to look next would be greatly appreciated

Should have a fused spur somewhere with a 3 amp fuse inside, looks like a light switch with a small square where the fuse fits, start searching.