Boiler pressure high - Glow Worm 30ci

[favemuppet]

Complete novice so forgive me.

Boiler pressure recently dropped and boiler shut down

Increased pressure as indicated to 1.0 bar (with heating off). When heating come on, pressure goes right up to 2.6 bar, then drops to 2.0 when goes off. Is this normal? Why does instructions say increase to 1.0 for it only to double when in use?

BTW - max pressure I believe is 2.7bar before boiler shuts down.

[htg engineer]

Pressurising to 1.0 to 1.5 bar is what is recommended, the pressure will increase slightly when the heating is being used, keep an eye on the pressure gauge over the next few days.

Why did the pressure drop to zero ?

Is there a leak, or did the pressure rise 4.0 bar and then open the pressure relief valve ?

if this happened then there couod be a fault with the boiler, either cold/hot water is mixing with the heating water causing the pressure to rise then discharge outside or the expansion vessel needs re-pressurising or replacing.

Most boilers have a pressure relief valve, which will allow the pressure to rise to about 3.0 - 4.0bar before shutting down the boiler.