Boiler reaching 3 bar and drops to 0 when off

[Famer23]

Hi,
I have a baxi boiler which is two years old. It only needs to heat 3 radiators.
The last few days, the bar has dropped to 0 overnight. When topped up to around 1 bar it starts fine and heats up. But it starts to go into the red zone and at just under 3 the release valve kicks in and water is released. It does this for a bit until the bar reaches 2. Then the heating works fine and doesn't creep back up. Then when the heating is off, the bar slowly drops back down to zero. And have to do the same process again. Any advice woulld be greatly appreciated. I have noticed a tiny leak from one of the pipes to the radiator. Could this be the cause? Or expansion vessel? Thanks

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[Harry Bloomfield]

Check the air pressure in the expansion vessel.

 

[Nozzle]

A combination of:
a) that leak (which causes pressure to drop off)
b) the expansion vessel bladder needs pumping up again (which causes the pressure to rise very fast once the heating starts).

Nozzle

 

[Harry Bloomfield]

A combination of:
a) that leak (which causes pressure to drop off)
b) the expansion vessel bladder needs pumping up again (which causes the pressure to rise very fast once the heating starts).

Nozzle

My thought is because it blows the water out so quickly and out of the PRV, it must be the expansion vessel.

 

[Madrab]

A tiny leak in the system would just allow the system pressure to drop slowly over a matter of days and wouldn't cause the system to over pressurise.

If when the heating's on the pressure rises sharply to >3bar, activates the PRV and then it then drops to 0 when the system cools down that certainly points towards an expansion vessel that needs re-charged.