If you have a Combi already its very likely that you already have 1 bar or more ,i doubt it would operate on anything less.
The 1.9 bar i assume your referring to is what the needle on the gauge is showing on the front of your boiler this gauge shows the water pressure in your heating system ,which should be on around 1 bar when cold then it will rise up as the water in the system expands as long as its not in the red its OK.
if you had less that 1 bar i think you'd know about it - the pressure would be appalling. i have 3 bar where i live (well, at 3am anyway! peak times it's closer to 2 bar) and it's only just about tolerable.
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