A heat sink is a thermally conductive heat exchanger used to quickly absorb and disperse high temperature heat away from a Primary Heat source.
A heat sink will stop a boiler or Primary heating source such as a boiler from thermally shutting down and can be positioned anywhere in the Central Heating circuit.
It is important that any Appliance or Secondary Circuit being used as a heat sink is at least equal to the KW heat output you are trying to remove from the Primary heating circuit.
If central heating radiators are being used to dissipate heat they must be sized correctly as excessive heat might make that room very uncomfortable to live in.
The most common place to install a heat sink radiator in a small property is in the bathroom because a bathroom radiator can remain on all the time to dry off towels but please check that the output of the bathroom radiator has enough output to be sure it can dissipate the heat required from the PHE quickly enough.
It is recommended that any radiator being used as a heat sink has a full flow of water flowing across it using a lock shield radiator valve on both the flow and return of the radiator rather than a thermostatic valve on the flow that opens and closes according to the room temperature.
Using a lock shield radiator valve on the FARAL radiator flow and return will stop anybody from adjusting the valve setting from fully open and allow the central heating water to circulate unrestricted through the radiator dissipating all the heat required from the heating system thus avoiding overheating and damage to the boiler and associated controls.