hi my vokera combi boiler has hot water but no heateig?

Hi im terry. Can anyone help us. Our boiler kept losing pressure, daily. Now its on 2 bar and the heating fires up randomly but not enough to heat our flat. Ive tried bleeding a couple of radiators and the spat black water out immediately.any help would be gratefully appreciated, before my hormonal pregnant girlfriend takes the boiler outside and has a ritual burning of it lol. Thanks Terry.