I always thought a potboiler was something one read that kept one so entertained that the pot boiled without notice. But no.
A pot boiler is a work of art created only to put money in one’s pocket and food on the table. Quick, low quality, cheap. It’s considered synonymous with pulp fiction and any of several more pejorative terms. I was mixing up who’s pot boiled and when.
But a pot boiler is also an early steam engine component. A pot boiler is a sealed cylinder that holds water under pressure while it’s heated at a low heat from outside. It’s the simplest type of steam boiler, it turns out; one that is easy to build.
It does tend to explode, of course, which is why other types of boiler (you can read about all the types of steam boilers here: http://www.southernsteamtrains.com/manual/boilertypes.htm) were created.
I’m still trying to unite both images into one metaphor.