Baxi boiler - No heat but hot water and very noisey?

It is my friends heating system. She has a Baxi boiler not sure which one, but has a tank in the airing cupboard. Last year it was making the noise of ticking bomb (when on heating). This year when she goes to use the heating there is a lot of banging noise from above the boiler. The heating will now not come on and the pilot light seems to be trying to light and then goes out...The hot water is working fine!!! The boiler is wall mounted in the kitchen. A engineer has been out and stood and scratched his head and didnt know, hasnt come across anything like this!! (helpful) to make matters worse my friend is a single parent and now has no heating... Help!!!!