whistlenut wrote:Having two AA 260's running 24/7-365 in a ten apartment complex, I can tell you tank-less coils will provide plenty of domestic hot water, HOWEVER the demand, once satisfied, makes it impossible for a boiler to 'ramp down' quickly enough to prevent overshoot....and overheating. Doesn't matter who's boiler it is.....so, a dump zone......or use of a big indirect and some tankage sure helps out. My 520's and 900 were set at 4 clicks, 4.5 air burning buck. AHS, AA, Keystoker and now LL work just fine without major adjustment.
Remember, this is a perfect time of the year to shut it down, clean stack piping, replace as necessary and vacuum out the boiler and passages.
I never had the 900 making steam after "overshooting" on a big DHW run. Are you saying there's no difference between the EFM and AA-type boilers on this? In another thread it was discussed in detail how the fire being in contact with the boiler vessel (as I understand it is in an AA) differs from the EFM in terms of heat transfer at idle.