raven heat boiler 4 years old ?

i have a raven heat boiler 4 years old , its not worked for the last 3 years really .. but we have mab do till now .. when i have it on hot water and heating . the heating works but the water will only run very slow or it runs cold , but the rads get hot .. if i run just the hot water its better but still the water is luk warm and just the towel rail gets hot at times .. i have had 3 plumbers out and they said i need a new boiler . but i cant aford a new one . can you help