gloworm fuelsave mk2 60b

hi all, have a gloworm fuelsave mk2 60b 24 years and was going strong, hot water fine radiators lovely and hot, working on y plan, have new pump and have changed the by pass,
only problem is boiler sound like a jet engine on the burn,
me thinks heat exchanger manked up, i have sentineel x200 in system has made no difference, i know you are going to say, bit the bullet and replace boiler, (and i will ) but is there any merit in giving it a dose of sentinel f3

regards to you all david

Use ds40 or you could just let an RGI replace the Heat Exchanger. 45 min job without the draining / refilling.

Flooze.