I have no hot water coming from my taps and the radiators are not heating up. When the boiler is turned on it makes a kind of rattling buzzing hum (i have no idea about this sort of thing). There is a sticker on the boiler that says the pressure should be at least 0.7 bar, and the pressure gague reads 1.5. The boiler is a gloworm swiftflow with an SIT valve. I dont know how old it is, however i've lived here for 3 years and its been here that long and was last serviced when I first moved in. Any help would be appreciated.