How can I fix my Ravenheat RSF820/20 T combi boiler?

I have a Ravenheat RST82/20 T Combi boiler, my radiators were not warming up so on inspection I can see the pilot light has gone out, this has happened before and just holding the ignite button in for a short time, then releasing it sorts it out. however, I have held in the button until the pilot light comes on but when I release it to ignite the boiler the pilot light just goes out. I have tried on several occasions with no joy. Of course it has to pick the coldest day of the year to play up doesn't it. Please can you advise me if there is anything I can do.
Many thanks