what is wrong with my Boiler ICI CALDAIE Solar Micro 24F?

I have a boiler that i had fitted in my house just over 2 years ago by a plumber. It is a ICI Caldaie Solar Micro 24F. The problem with it now is that it does not give out any hotwater unless you turn the central heating on. I had one plumber look at it who told me it might be the diameter bulb? (I am not a plumber so do not have a clue what if anything this is) he further told me that he couldnt source the part needed to repair it from his local supplier. I was unable to find the plumber who originally fitted the boiler. Does anyone know if this sounds like it could be the problem or does anyone know where in the UK i could get advise or find parts for this boiler? has anyone owned or repaired this boiler and had this problem before?

Thank you in advance for your help.

Harvey
November 2008