I need a bit of advice. I have a 17year old ideal c28 that the primary heat exchanger has been kettling for a while but now its got really bad . The system has been flushed and cleaner put in but it’s not helped so have it booked in for the exchanger to be replaced. The person who looked at it has advised that although not much came out when the system was flushed I should have a filter fitted at about £200. Do I really need this and if so any recommendations?