Hi all,
does anybody perhaps know which part of the GS/3 needs maintenance, I have turned off
the steam boiler, however every two days (predictable) the steam boiler is refilled for a
very short amount of time (perhaps one second). I suspect that backflushing somehow
drains the steam boiler.
The probe seems to be ok as the steam boiler does not overfill.

Thanks for any hint!

Not sure why the boiler cycles, but I believe it's harmless and I wouldn't worry about it.

My GS/3 auto-fill usually comes on when the machine is turned on, even though the steam boiler was full when the machine was turned off (and, presumably, while the machine was off the steam condensed back into water and raised the level!) I believe either the CPU does this as a safety feature (and maybe periodically when the machine is on), or there's an evaporation path for water vapor when the steam boiler is off, and that this gradually causes the water level to drop just enough to kick on the auto-fill.

Before I get into more detail on this possible evaporation path, note that due to the positioning of the probe on the boiler and the relatively short probe length, there's not a lot of headroom between "full" and "fill needed". If the probe set an an angle to the water level (i.e., isn't pointing straight down into the water), you have even less headroom. The angle of the probe can be changed by loosening the lock nut and turning the connector. When the connector is facing straight down, the probe is too. That's the maximum headroom you can get. Even then, it isn't a lot, so it won't take much of a drop in level to kick on the auto-fill.

As I said, I think the most likely cause of the drop in water level is that some of the steam boiler water is evaporating. Even though the steam boiler is off (and I have some questions and advice on that below), the steam boiler is still in a very warm environment. Heat radiated from the brew boiler warms up the inside of the machine and will eventually be conducted to the steam boiler and the water inside. That will result in faster evaporation.

Also, the brew boiler heat exchanger runs through the steam boiler, and will raise the temperature of the water, which isn't being heated to a higher temperature by the steam boiler's heating element. So, when you brew and backflush, you're raising the temperature of the steam boiler's relatively cold water, and this along with the ambient heat from the brew boiler might cause enough evaporation to kick on the auto-fill.

There's plenty of room for water vapor inside the steam boiler, so it's certainly possible that it doesn't take much evaporation to drop the level. What's more, there's an escape path for the water vapor: the vacuum breaker valve, which is wide open when the steam boiler isn't on (i.e., under pressure.) So, over time, water evaporates, the vapor escapes through the vacuum breaker, more water evaporates, and the water level drops. So, ironically, by turning off the steam boiler you may have increased the frequency of auto-fill. Just a theory.

Now, as to your steam boiler being turned off, how exactly did you accomplish that? Did you lower the temperature setting to the minimum? That's not off -- it'll still heat the water, which will cause even more evaporation. Or, did you pull the AC connection to the steam boiler heating element? If so, I hope you insulated the live contacts at the ends of the wires.

If you did either, you may have defeated perhaps the most important feature of the GS/3, which is its temperature stability. As mentioned above brew water is pre-heated via a heat exchanger that runs through the steam boiler. At a minimum, you are increasing the recovery time between shots. If you don't pull a lot of shots that's not a big deal, but my concern is that you may also have affected the intra-shot temperature stability by removing the pre-heatiing. Arguing against that is the fact that the GS/3 Shot Brewer doesn't have a steam boiler or heat exchanger. But it's also possible that the PID parameters are dependent on whether a heat exchanger is present or not, and may need to be adjusted to compensate for it not being in the path anymore. Others on this forum know more about this than I do.

Dick, thanks for your reply!
I have the GS/3 for five years (steam boiler temp set to 20C most of the time, except for some
occasions when it is turned on), and these symptoms have started only recently. I should perhaps just
turn on the machine for two hours every day without making espresso, and look what happens.
And yes, you are right about the temp. stability, but it is good enough for me even if the steam boiler
is turned off.

Some other thoughts -

The GS/3 has three settings for steam boiler water level probe sensitivity and I would ASSUME that the middle one is the default. Is it possible that this was inadvertently changed ?

It may also be POSSIBLE that the properties of your source water has changed because of a tired filtration system.

As a point of interest, but not applicable to your situation, steam boiler water volumetric levels at 75F (~23.9C) will be about 94% of those at 260F (~126.7C).

Good points, Eric! I hadn't considered the probe sensitivity setting and the water composition. Definitely worth a check.

And I had also forgotten about the water volume being lower at lower temperature. I'm not sure sure that's not applicable. If one of my theories is right, 6% less volume would put the water level that much closer to losing contact with the probe, such that a very small amount of evaporation might take it over the edge.

Probe sensitivity is set to LOW, no change in the past. Volvic water is used. It could be an issue
with the level probe, however as I wrote, the boiler does not overfill, and it seems some water
is actually pumped into the steam boiler during the short refill cycle (which is perhaps one second),
there is some water noise It seems the probe is accurately maintaining the water level (theory
falls apart of course if no water is pumped during the refill cycle).

LM has really good customer service. Just sayin'....