Best Of

there have been cases of the diaphragm being stuck in expansion tanks. Stuck against the nipple of the connection. Increasing fill pressure may pop it off. But remove and check pre charge first.

The more condensate you get the higher the boiler efficiency. I’m surprised you see that much with a fin tube system.

If it is piped with copper? It should not have a lot of water capacity, a #30 tank should be adequate.

Tune the boiler as others mentioned. A heat load calc would tell you if it is an energy hog structure.

The control should have other functions to dial it in, ramp delay, anti short cycle, burnrr limit, boost function? It varies from brand to brand.

Yes the 74 degree indoor will cost more than degree.

1. Run time is too low. See about limiting max fire %.
2. Lower supply temps
3. Condensation is the goal. Did you read the manual?
   

Performing a combustion analysis with a digital combustion analyzer during minimum and maximum firing rates is a critical step in the start up procedure of any condensing boiler. This is in the installation instructions and is not supposed to be ignored.

The expansion tank air pressure needs to be charged to the static pressure of the fill valve before installing the tank. If you actually did this and you still have pressure increasing near 30 PSI while the boiler is operating the tank is too small. Sizing information is available from the expansion tank manufacturers.

Install a condensate pump and neutralizer.