How can i fix sime friendly combi boiler?

i have a sime friendly combi boiler (sorry, dont know model number). the central heating is working fine, the problem is the hot water. i haven't got any...
when you run the hot taps, any of them, the water is tepid to say the least. pressure is rising to 3. also, don't really know what any of the dials on the front are for. i have 2 switches. 1 with clock and dot, the other with what appears to be a "sun" and a "snowflake"
i then have 2 dials with the same small to large arrow on them. can anyone enlighten me?
thanks for your time
sam