Firebird 90 oil combi boiler?

i have a firebird 90 combi boiler. I very rarely use it to heat the water as I have a seperate electric shower and I live alone. I fancied a bath this afternoon so I switched on the water. The central heating went off which I know it does. However the water did not heat and the green light would not go out. Eventually it went out and the heating came back on but after two minuted the limit stat orange light came on and the heating went off and the water too. Any ideas Linda