boiler fusible plug failure

The job of the fusible plug is to act as a final resort to poor boiler water level management and prevents the boiler from exploding.

As an illustration, on a steam railway locomotive a fusible plug is present as a fitting in the firebox crown plate. With good water level management (the job of the fire[wo]man) the fusible plug, which is exposed to the heat from the fire in the firebox, is kept close to the temperature of the water above it. If the water level drops low enough to expose the fusible plug to steam instead of water, the temperature of the plug will rise, the inner part will melt, and the contents of the boiler will very quickly vent via the firebox, a spectacular and very hazardous event that, should the crew survive, provoke demotion or dismissal. Were the fusible plug to be absent, the rising temperature from low water level would eventually cause the softening of the firebox crown plates, from which a catastrophic boiler failure can be expected with casual damage to most objects within a wide radius and destruction of the locomotive.

http://en.wikipedia.org/wiki/Boiler_explosion

should the crew survive, The plug is there so that the crew will survive

Baling the fire out while the firebox is filling up with vented steam? Stuff that for a game of soldiers!

Sorry: "If the crew stays on the locomotive". Let's try that instead.

Too much heat.

In his eloquent answer, PWSlack illustrates a very important point. Your problem is not a problem with the fusible plug. It is a problem with proper maintenance of the water level system. As PWSlack points out; this is a safety issue.

The water level sensor and reporting instrument (even if it is only a glass sight gauge) are seriously out of tolerance and should be calibrated and adjusted as soon as possible before some unknowing mechanic attempts a "fix" and replaces the plug with something more substantial (the resulting explosion may eliminate your need for an answer from this forum).

Check fusible plug for quality of metal & improper filling.

Increase water level in the drum after careful study.(Provided your basic water management is alright.)