BAXI BOILER?

Hi I hope someone can help, my (very nice Mother in-law has a Baxi solo boiler, she has had this for about 3-4 yrs supplied through British gas. the boiler has been fine up until recently. When the hot water is turned on the radiators come on, not all of them just a few. The hot water also does not seem to be getting that hot either although she does not seem to have it on that long.
Thanks for your help.