I hope you mean 0.4 bar and not 4 bar. Most residential heaters are
supposed to be less than a bar. Shut it down and call a repairman. Thee is
a pressure switch that may be out of adjustment or may have gone bad and
needs replacing. If It is 0.4 bar, you are in safe limits, if it is 4 bar,
the pressure relief valve should have gone off.
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