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I have a Viessman Vitodens 100-w which keeps losing pressure even when the device is completely turned off. If I top it up to 1 bar pressure, within about 20 mins it goes down to 0.5 bar and stabilises at that level. There is no sign of water leak anywhere in or around the boiler or the house...

Hi I have a Viessman Vitodens 100-W combi boiler WB1B If topped up to pressure 1 bar when turned off and cool, it goes down to about 0.4 bar after 1-2 hours. when it runs, it can properly heat up the radiators and provide hot water but the pressure keeps raising and rising and can sometimes go...