Ariston Bolier Trouble

I have had a Ariston Bolier for some time now. But recentley it has bee
giving me some trouble so i blead some water from the radiators. Bu know the water preassure gauge keeps hitting 90% then switches cool down and hits 90 again what should i do ?
I have filled the boiler with water but it seems to make n differance.
please hel
-- hsj123
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