downstairs radiators cold

I have a mft140 thermal store and getting no hot water, however water is coming from the waste pipe when I run the taps

Hi, I have just had a service on my boiler and they have suggested a flush of my system as the water is dirty and some of my radiators seem to have build up of sludge. Could I get a price for this please? If you need any more info let me know, i live just off anlaby road

I have a Worcester ri 24 installed which is now about 10 years old and needs replacing with a ri 12 model

11 radiators including towel rails