Water pressure increases at taps when heated

Hi readers,

Last year I had some plumbing upgrades done. I got the plumber to turn my plumbing system into a closed pressurised system.

• There's a pump that runs when the taps are turned on. The pump is out in garage with its own expansion tank.
• There's a new hot water tank with its own smaller expansion tank.
• There's a pressure valve that can be adjusted. I keep it low at around 1 bar. This gives a reasonable flow rate at the taps.
• I also got the oil heating zoned into two zones (rads and hot water tank).

However I notice when I heat the water tank (emersion or oil), As soon as I turn on a tap, there's a blast of very high pressure water from it for about 7-10 seconds, then it runs normally.

Is this increase in pressure ok? I worry that its causing a breathing effect on the entire plumbing system and may cause a failure. Maybe its perfectly normal, I'd just like to know.

Many thanks for reading