You are welcome, "Steam Pressure Relief Valve" is not a phrase that readily springs to mind.
In your situation things are not so bad. The Hot water unit actually is not sealed even though the tap at the sink is closed.
The inlet pipe is still open and theoretically, any build up of steam from a faulty unit could have a relief route pushing the water in the inlet pipe all the way back to the village supply, relieving the pressure in your unit.
Don't know how your neighbors would feel about having hot steaming water coming out of their cold tap. ????