Combi boiler. not working. the gas light comes on and the heating, hot water and pressure work fine but?

the boiler is making gurgling noises (kind of like a kettle boiling) as if there's too much water and the boiler itself is making t noises after about 5 mins of hot water tap being put on and the heating also. i've tried resetting it, i've tried switching it off altogether and then back on i've tried bleeding the radiators and adding extra pressure but none have helped. i'm at a real loss now cause there is no heat as i fear the t noises are going to be doing more damage. any help would be appreciated A LOT!!!!!!