24i Worcester RSF Combi - hot water but no heat!?

Hello - It's regarding the boiler mentioned above. I am getting hot water easily enough but no central heating. It sounds like (although I know virtually nothing about this kind of thing) the ignition isn't happening when I turn on the heat or try and manually override the thermostat. The thermostat is a towerstat rsp. Regarding thermostat - battery is fine. It's displaying 14 degrees (I can see my breath). Boiler has a summer setting so that it only supplies the hot water - it's not that as I have the dial turned now on to maximum. I can't reset the boiler as the reset button hasn't popped up (I read on this site somewhere that if it's not able to be pressed down, it's not necessary to reset which is good as I can't figure out what you would do to reset it anyway). The pressure is 2.5 bars which is the maximum setting. It was previously about 1.3 but I raised it to 2.5 before trying to fix the problem. I don't know if this makes sense to anyone but I would be extremely grateful if someone knew what I could do...do I need to reignite the pilot or something? I just had a shower and left the hot water running for a bit as I read another post that said their boiler kicked in when they ran the hot water for a while, but it didn't work. I have the manual for the boiler (http://www.r-and-m.co.uk/Downloads/24iInstallationManual%5B1%5D.pdf) and the manual for the thermostat (http://www.jaysafe.co.uk/technical/towerstat.asp). As I said - I'm extremely grateful for any advice as I am really struggling to sort this on my own and don't have much money to fix it!
THANK YOU!