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Not normal, if sized correctly and with precharge&filling pressures of 1.0bar/1.5bar when cold, should not rise to more than 1.8/2.3 bar when hot.
If a external E.Vessel what size is it ?.
If a combi boiler might be a leaking HW heat exchanger causing mains water to pressurize the primary water side.
Reply to the thread, titled "Hi all our boiler has just had a new expansion vessel fitted but pressure is still going to 2.9 bars when using central heating . Is this normal? Than" which is posted in Boiler Advice Forum on Plumbers Forums.
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