The thermostatic safety valve is a safety feature with the boiler. It is connected via a cold mains water feed to a cooling coil that runs along the top of the boiler. If there was a power cut then if the temperature of the water in the water jacket reaches 95 degrees Celsius the valve will open ensuring the flow of cold water through the cooling coil to maintain a safe temperature for the boiler until the wood in the loading chamber has burnt out or the fire has gone out.
It is a self-acting principle requiring no external power. The thermostatic safety valve will operate safely regardless of the ambient temperature and the self-acting technology means that the valve does not require electricity or other forms of energy in order to work.
There is a test button that enables periodic testing of valve.