What is the purpose for the restricters in a hot water heater?

Answer 1

It really depends where the restrictors are and what you determine a restricter to be.

Depending on the pressure in your pipeline, some hot water heaters will need pressure to be reduced as the manufacturer will only warranty their cylinder up to a certain pressure.

Other than this being the answer, you will have to explain where the restricter is.

The reason for the restriction is as follows

1- To prevent stratification of the hot water entering the cold water supply line as many installers are ignorant about installing a thermo loop of 27" on the C/W piping

2- Another type of restriction is used to monitor the flow of water exiting the heater so the GPM demand does not exceed the output capability of being delivered.

If the flow rate through the heater is 8 GPM and the heater can only produce 6 GPM of heated water then a flow restrictor can allow almost an unlimited supply of heated water

A flow restrictor is not the same as a pressure regulating device.