I have a Baxi 100HE that is VERY noisy on startup to the extent that you can hear it outside the house due to noise coming from the exhaust pipe. The noise last for around a minute and then subsides. After this it is reasonably quiet and well-behaved. The loud noise happens only on a cold or relatively cold start.
Do you think this could be cleared up by flushing the system and refreshing any additive? It has not been serviced since new 3.5 years ago...? It has Detz Dearborn inhibitor in and has 12 radiators hooked up to it.
Thanks
John Holbrook