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Burnham Alpine boilers - DHW questions

t_6 Member Posts: 6
This is a follow up of sorts from my previous question back in January (<a href="http://www.heatinghelp.com/forum-thread/134368/Boiler-piping-configurations#p1216447">http://www.heatinghelp.com/forum-thread/134368/Boiler-piping-configurations#p1216447</a>).  

I have an ALP80 boiler w/ AL50SL water heater serving one apartment, and an ALP105 w/ AL50SL water heater serving another apartment.  The installation on each was incorrect.  They have now been completely re-piped by a different plumber, and the piping and new pumps appear to be exactly as per the Burnham manual.  A couple of new issues though:

1. During a DHW call the ALP80 runs continuously at normal modulation (~4450) until the demand is satisfied.  The ALP105 though is short-cycling during a DHW call.  I was finally able to stop this by adjusting the DHW max modulation to ~2250, but I don't understand why there would be this difference between the two boilers -- the piping configurations and DHW circulator pumps are identical (water heaters as part of near-boiler piping, Taco 0014 pumps).  Is this indicative of a circulation problem?

2. During a DHW call, as the supply water heats up I can hear what sound like air in the water.  The air separator is installed on the manifold as per the Burnham manual, but this appears to be out of the flow of water during a DHW call.  How is this air purged?

3. On the ALP105, I will occassionally hear a louder-than-normal "whoomp" during ignition and then faintly smell gas (I think).  This obviously needs to be looked at, but what sort of issues could cause this?

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