A double boiler is a two pot cooking device. The bottom pot holds water. The top pot is smaller (usually with a lid) and fits into the bottom pot. When the water in the bottom pot gets hot and boils, it then heats the top pot thereby warming or melting or cooking what is in the top pot. This same device is also known by the french "bain marie".
A double boiler is used in cooking to gently heat and melt delicate ingredients like chocolate or butter without burning them.
A double boiler is usually used to melt choclate. You can make one yourself by using two pots and boiling water.
Gluepot
Finding a quality double boiler has been more difficult in recent years. Double boilers aren't as popular as they used to be. Look for one made by a reputable manufacturer, and one with a thick, well insulated bottom.
Double boiler
A double boiler is used for this. It can also be melted in a regular pan, with water, on a very low heat.
I would recommend using a double boiler. If a double boiler is unavailable, I would heat it on low heat and stir it frequently.
Pasta needs to cook in rapidly boiling water, so a double boiler won't work that well for cooking pasta.
that depends use for what
An auxiliary boiler is a secondary boiler used to support the main boiler in a steam power plant or marine vessel. It is often used when the main boiler is unable to meet the steam demands, providing additional steam capacity. Auxiliary boilers can also be used for heating purposes during maintenance or downtime of the main boiler.
Boiler
One may decide to purchase a used boiler because of the lower price for a used boiler compared to new boiler, in that case one will have to compromise with the quality of the boiler.