Excellent and informative post spudnuty!
I'm not sure what country the original poster is from, but here in the US it is extremely rare to have a pressure regulator on the feed line to our homes (except in very unusual circumstance) but their is always a regulator to drop the feed pressure to the hydronic heating furnace, along with a pressure/temperature relief valve (as required by code). Hot water heaters are also equipped with a pressure/temperature relief valve and a vacuum breaker device (as required by code), but not usually with a pressure regulator.
The amount of pressure in our hydronic home heating system is determined by the altitude of the upper floors of the home, which is nominally about 13 psi, hence the pressure regulator feeding water to the heating system when needed is set to a value nominally above 13 psi.
Our hot water heater is a separate gas fired unit from Sears (nothing special) with a 50 gallon tank, and is rated for a tank pressure limit of (I just checked the label) 150 psi. Since our water feed pressure from the street is nominally 45-50 psi, there is no need for a feed water pressure regulator on the hot water heater, nor is such required by code.
Sorry about the use of psi rather than bars, but all our current heating devices are labeled in psi.
Kindest regards, Harry C.