My Vaillant 242E is not producing enough hot water, engineer says heat exchanger prob. scaled up, not worth replacing, wants to instal new, larger boiler. Boiler about 15 yrs old & the ONLY problem in all that time has been DHW heat exchanger, which was replaced a no. of years ago. This has been such a brilliant reliable boiler and I DON'T want to replace it. Unfortunately the guy who installed it has moved on & he was the acknowledged local Vaillant expert. My feeling is that most firms have a standard policy to recommend boiler replacement for old boilers, but my policy is to keep a good machine running, like my brilliant 12-yr-old Nissan car. Any Corgi engineers in Norwich area willing to do this job ?