Baxi Eco 80 Combi Boiler?

Hopefully someone can help me. I have a Baxi Eco 80 Combi Boiler, last week the CH always ON, even I turn the switch to hot water only, but the still on, That make my house like a oven, I just can use for when I need hot water turn the heater ON then finish turn off, anyone can tell me what happen. Please.