Hi, I've been lurking for quite some time and I have definitely picked up a lot from the knowledge on this forum. Cheers to everyone involved!

I am completing my Giotto rebuild and have encountered a problem with the boiler pressure (I think). My machine is only heating up to a group temp (Eric's Digital Therm.) of about 203*F. My p-stat is cycling between .85 and 1.25 bars (pretty large for the CEME, right?). I tried flushing to about 193-194* and then pulling at 198* on the way up (which takes quite some time) and the shot was over-extracted. During the shot, the temp. jumps up to about 207-210* and then drops to about 203* and finishes around 200*. I'm using Barefoot's The Boss (not quite dialed in, yet), the taste is off and the crema is pretty dark. During the last shot I pulled, the pressure went crazy and pegged the needle -- at least I know the safety valve is working. I immediately shut off the machine and now am at a loss as to what's wrong.

I'm thinking that the p-stat is bad or maybe my boiler pressure gauge? I fixed all the small leaks during reassembly and have adjusted the brew pressure to about 135-140 psi (flutter). I believe I've got my p-stat set at 1.25 bars (according to my gauge) but sometimes it kicks off at 1.1 and sometimes at 1.3-1.35.

Any help would be much appreciated. I have a spare p-stat that I'm going to test out but after that I'm not sure what to do. Thanks again!

Matt

Ok, so my thnking was a little clouded last night with frustration and Sierra Nevada Torpedo. I now think the problem is the boiler level probe. I'm thinking the probe is triggering the fill solenoid to open during the brew cycle. This is causing the boiler to fill faster then the p-stat can react and the pressure is built from the water/steam combo having no where to go. Does this seem accurate? I don't believe the boiler should fill during the brew cycle because the water level isn't changing (negligible).

2 quick questions:
1) I discovered a very slight drip coming from the group and exiting between the frame and front panel. Is it ok to use thread tape on the non-compression connections?
2) Will small leaks like this cause my group temp. to be lower?

Thanks!

Matt -

I would suggest you fix known problems first. The boiler pressure swing you noted is, as you say, rather large and the fact that the boiler pressure "pegged" the gage at one point is indicative of an ill pstat. The CEME pstat typically has a smaller deadband than others but not by much. By that I mean that CEME might be 0.15 to 0.20 bar whereas MA-TER might be 0.20 to 0.25 bar. Even so, I find the MA-TER far easier to adjust but that is something you usually do only once and should be performed with the machine fully up to temperature.

Ideally, the boiler should not fill during a brew cycle but keep in mind that the boiler fill circuitry also has "deadband" built into it. FOR EXAMPLE ONLY: Say that the design water level in your boiler was 3.00" as measured from the bottom. The fill would activate when the level remained at 2.99" (probe uncovered) for a fixed period of time - say 2-3 seconds. The fill would also run for a fixed period of time (say 2-3 seconds) after the level was satisfied (probe covered). Maybe look at it as a random pressure profiling event

A boiler fill will slightly reduce the overall water and steam temperature momentarily but the effect on pressure is negligible.

The drip you notice is, I BELIEVE, coming from the cylindrical container surrounding the boiler safety valve. Is the safety valve leaking? A pic would be helpful.

I don't believe the safety valve is leaking. It appears that the leak originates on the lower group head connection and then drips between the frame and the SST face plate, so I've decided to disassemble and then rebuild -- again. I did notice that the lower connection (90 degree fitting) has a crush washer on it. Should the upper connection (3/8 male-male) have one, too? During reassembly, any reason not to use teflon tape on the non-compression connections?

Besides a minimal difference in the deadband, is there really any other difference between the CEME and MATER p-stats? And is there a difference between the all black CEME (stock La Marzocco) and the black and yellow one? I'll also be replacing the boiler level probe, if for nothing else but knowing that the part is good.

Other than that, the safety valve, vacuum breaker and safety thermostat are new. I also replaced the OPV with the same as the Quick Mill machines and added a new 52W pump. On top of that, I rebuilt the wiring harness because the old wires were a bit crispy. Anything I'd be missing?

Thanks for the help!

Cheers,

Matt