They both leaked combustion gases inside the cabinet.
Causing all kinds of trouble. Second one said it was bad installation. Oddly it was installed same as 1st.
Put in Well McLain going on 11 years no trouble at all.
Good luck with your Navian boiler.
I've had 2 of them self destruct in less than 5 years.
Company wouldn't honor warranty on 2nd one.
See Mikey Pipes Plumbing on You Tube.