Hi. I have a giotto evoluzione. Have a problem with the group head pressure gauge it rises on standby up to 9bar without the pump. If I start the pump and stop it, it resets the gauge to zero. And I don't think the brew pressure is there when pulling a shot. Machine is only 3 months old. Any ideas?

That's normal.

That is, pulling a shot introduces cooler water into a closed system, but then you suddenly close off the main exit at the end of the extraction. As the water in the heat exchanger warms up, it expands and the pressure rises. The expansion valve is typically set to open around 12 bar for rotary pump espresso machines since they have their own bypass valve to regulate brew pressure. For vibratory pump espresso machines, the expansion valve (traditionally called an over-pressure valve in this context) is set to open at the desired maximum brew pressure, usually around 9 bar. This valve vents water to avoid subjecting the hydraulic system to excessive pressure.

Thank you for the reply. But it's first time it has done it. Take it I'm worrying about nothing??? Even when I back flush the pressure won't go over 8.5 bar

If the brew pressure doesn't rise to ~9 bar against a blind filter basket, then the pump pressure needs adjustment. Rotary pumps adjust via a bypass valve screw; vibratory pumps adjust via an over-pressure valve (search the forums for instructions). Note that for rotary pumps, a change in inlet pressure changes the resultant brew pressure; if the inlet pressure isn't constant, a pressure regular is required.

Just a wild guess, but have you descaled lately? Because scale buildup has a way of making espresso machines behave oddly as valves stick open, stick closed, or randomly stick. Scale buildup can also mess with the brew pressure reading (e.g., as discussed in Lethargic pressure gauge).

I thought that have descaled it today. Do you often have to re dial the pump in?

Hi there.

I have the same machine (Cellini body type). I assume you are talking about the dial in the right that indicates the pressure at the pump outlet...

I've checked mine today and the dial stays put during idle time (pump not on). Following a shot or a backflush, it does not go back down to zero, you have to engage the pump when there is no restriction at the brew head for the dial to go back to zero.

However, once it's settled on a certain pressure and the pump if off, it never moves.

I would agree with Dan, there might be something wrong in the pressure gauge assembly, in particular the little pipe leading to the gauge (scale, air, etc) that is causing this weird behaviour.

Give the descale a go, maybe if your water is really hard there could be scale after 3 months. If not, you might need to have the gauge taken out and inspected. I think there are a few threads on the subject in these forums if you want to do it yourself.

Antbunt wrote:...Do you often have to re dial the pump in?

If it's fed by the tank, no.

If it's fed by a water line, yes if the source pressure has significant variations.

Thanks for replies. It's tank fed. I think it may be scale. Calling the suppliers today they are really helpful.

Update. Spoke to engineer today. Apparently it's a common problem it's one of the valves sticking. Told to descale and back flush. It should clear.