Leaking water - because combis work under pressure, any iffy joints will be found out - trace the leak and have it re-joined.
Lighting pilot - try running the hot tap whilst keeping pilot valve pressed in. Don't ask why, it worked for me. Try turning pump to max (3) to get water to high rads. Also, balance the rads - any good DIY site will instruct how. Good luck.
Phil D
January 2005