Before lighting up a boiler you should:
1) purge the furnace
2) open the blow down valve
3) check the fuel supply
4) fill the boiler with water
a) 1, 2, 4
b) 2, 3, 4
c) 1, 2, 3, 4
d) 1, 3, 4
e) 2, 3
Answer: D