Also, because HSB writes only boiler insurance, an agent does not need to be concerned about having to make a huge volume commitment of other kinds of insurance just to be able to use HSB's boiler and machinery insurance. There are several types of boilers. They are referred to with such terms as fire tube, water tube or cast iron sectional. Boiler inspectors and boiler underwriters need to know the differences among the various styles of boilers. A lot more than boilers are covered.
Fire goes through the tubes in the water to turn the water into either hot water or steam.
One of the safety controls on this style of boiler ensures that the fire will be turned off if the water level inside the boiler gets too low. In the above example, the low water cutoff control malfunctioned. Several of the fire tubes got too hot because there was no longer any water around them. So, aside from all the other damage from that accident, it caused several of the fire tubes to warp, so they had to be replaced. A boiler and machinery policy would pay for the cost of replacing those warped fire tubes.