I have a Gloworm boiler and I have got a plumber to look at it he said the heat exchanger needs replacing. Also the diverter valve. If the heater exchanger was not working would I still be able to get the heating to work?

I had a service on the boiler about three months ago and had to call them back as the water was not running hot on my combi boiler. The fault was rectified by cleaning the internals of the heat exchanger with acid. Would this be done during a service as I am now being expected to pay over 60 pounds for this. Any help would be appreciated