Then which phase does he wire the boiler circuit to?

IMO if this is gas heat just run one circuit. It's only 10 amps combined so the inspector cannot say anything about the load being too much for a 15a circuit.
If it is oil fired you'll probably need another to carry the load of the boiler burner motor.


Speedy Petey

"Anyone who has never made a mistake has never tried anything new." -Albert Einstein