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JPL941

Hello

bob eck

Before putting a boiler buddy on your system how many heating zones do you have? What type of system is it? Copper baseboard? Cast iron dashboard? Cast iron radiators? Duct coils? Steel radiant wall panels? Radiant?
Is the outdoor reset control wired into the boiler control?
If the outdoor reset control is wired into the boiler has the boiler control been set up?

hot_rod

Their manual indicates a separate circulator in the heating only boiler. The circ on board the combi should be plenty to give the minimum 6 gpm they require.

How does the low output match your heating loads? Use any and all control options to limit short cycling first.

If you do decide to buffer, I like a two pipe for that application. It gives you direct to load heating and also utilized the tank capacity best. That tank has large piping connections, should be a simple install.

A multipurpose air/dirt/magnetic sep at the boiler supply to the tank.

Here is a journal explaining the different piping methods.
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf

JPL941

Bello

hot_rod

Sounds like you chose a 155 more for the DHW output?
To make a 2 pipe buffer tank, plug all the ports you don't use on a 4 port tank

If you can guesstimate total water capacity size expansion tank to that. Amtrol and Wessels have free online calculators.
Easier sometimes to add a second 30 instead of replacing. a #60, or 2- #30 should be plenty.