Thank you to you all for your answers, really very helpful .

Peppersass wrote: If Bill Crossland sees this post he can answer the question.

So far it seems he did not...maybe it makes sense to write to LM directly and ask them about safety measures for the brew boiler. In an older Version of the programming manual I found the description of the folliwing error message:

Coffee boiler
filled?

This message is displayed after the boilers have been
drained. The CPU is verifying that the coffee boiler is full.

Fill the coffee boiler with water (see operating manual for detailed instructions). Ensure that all air is bled
from the coffee boiler using the air bleed screw atop each group casting. The CPU will display this message to
ensure that the coffee boiler is full before supplying power to the coffee boiler heating element.

I really wonder how that message could be triggered if there is no water level probe in the brew boiler.

@Peppersass: In Replacing steam boiler seals on the La Marzocco GS/3 I read that you removed and mounted the heating elements again. How strong do the nuts have to be tightened? Did you use a torque wrench?

redhood wrote:I really wonder how that message could be triggered if there is no water level probe in the brew boiler.

I've never seen that message. Maybe it gets displayed if you turn on the machine and the steam boiler doesn't fill after a certain amount of time. Again, there's no fill probe in the coffee boiler.

redhood wrote:@Peppersass: In Replacing steam boiler seals on the La Marzocco GS/3 I read that you removed and mounted the heating elements again. How strong do the nuts have to be tightened? Did you use a torque wrench?

There's no published torque rating so I didn't use a torque wrench. The techs at LM USA might know the torque rating.

I slowly screwed down the nuts alternately, like you would tighten the bolts on a cylinder head -- i.e., so they get tightened evenly.

There's a technique for tightening a nut without a torque wrench that I learned from a motorcycle mechanic: tighten the nut with gentle pressure (use fingers, not you're whole hand) until you feel the nut bottom out. There's a significant jump in resistance when this happens. If you tighten more than another 1/4 turn you'll probably strip the threads. With practice you learn what it feels like when the nut bottoms out.

redhood wrote:I really wonder how that message could be triggered if there is no water level probe in the brew boiler.

I've never seen that message. Maybe it gets displayed if you turn on the machine and the steam boiler doesn't fill after a certain amount of time. Again, there's no fill probe in the coffee boiler.

redhood wrote:@Peppersass: In Replacing steam boiler seals on the La Marzocco GS/3 I read that you removed and mounted the heating elements again. How strong do the nuts have to be tightened? Did you use a torque wrench?

There's no published torque rating so I didn't use a torque wrench. The techs at LM USA might know the torque rating.

I slowly screwed down the nuts alternately, like you would tighten the bolts on a cylinder head -- i.e., so they get tightened evenly.

There's a technique for tightening a nut without a torque wrench that I learned from a motorcycle mechanic: tighten the nut with gentle pressure (use fingers, not you're whole hand) until you feel the nut bottom out. There's a significant jump in resistance when this happens. If you tighten more than another 1/4 turn you'll probably strip the threads. With practice you learn what it feels like when the nut bottoms out.

I guess it worked out because the steam boiler seals haven't leaked since I replaced them several years ago.

Peppersass wrote:There's a technique for tightening a nut without a torque wrench that I learned from a motorcycle mechanic: tighten the nut with gentle pressure (use fingers, not you're whole hand) until you feel the nut bottom out. There's a significant jump in resistance when this happens.

Does that mean you can actually tighten the nuts until the brass plate on the heating element touches the boiler, without compressing the gasket too much?

Yes, there's no space between the brass plate and the body of the boiler. I'm sure the gasket compresses somewhat, but I believe since the opening is tapered it doesn't squash completely flat.

Why not give LM USA a call and ask them if there's a torque rating for those nuts?