Water coming out of vacuum breaker when machine is cool

[goodboyr]

Last night I found water dripping down from the bottom plug under the boiler during an "off" period. The machine was off and relatively cool. I pulled off the top cover and found the source, a one drop per second leak from the vacuum breaker. So as I understand it, that means the solenoid valve is likely passing, which caused the boiler to fill and then leak out the top of the vacuum breaker which is open when the boiler is cool. Turned the machine back on, let it heat up and pulled water from the steam boiler until the pump started. Did that a couple of times to cycle the same solenoid valve. Two questions:
If this was the cause, is it reasonable to think I've flushed out and debris and the sv fixed itself since there is no leakage or issues now that it's hot?
Or will this only show up when its cooled down and the breaker is open again?

[chas]

Water shouldn't come out when the steam boiler is hot even if there is still an issue since the VBV is closed at that time. You can't consider the issue fixed unless it still doesn't leak when the machine cools back down and the VBV is again open.

Most overfill issues are caused by the water level probe. Sometimes it gets pushed up and just needs to be pushed back down. Other times it gets mineral coated and needs to be cleaned. However, if the water level probe is the issue, I wouldn't expect a continual drip from the VBV since the closed solenoid should keep additional water from entering the boiler and then exiting the VBV. Thus your diagnosis that the problem is minerals clogging the solenoid valve sounds like a reasonable assumption.

Still, it's so easy to inspect the water level probe that you should.

[goodboyr]

Thanks. I guessed I thought that the water line pressure would still be high enough to over come the safety valve. I will check sensor and then do a cool down cycle.

[chas]

The water line pressure is present in the group boiler because the solenoid is on the output side of the boiler between the boiler and the group. However, the solenoid is on the input side between the pump and the boiler for the steam boiler and should block all flow except when the solenoid valve is open and the pump is running.

[goodboyr]

Agreed. But if my theory is correct that the solenoid valve is passing then it would present line pressure to the boiler and eventually pressurize it to line pressure. In my case that's 3 bar.

[chas]

If you had the full 3 bar pressure coming into the boiler you'd be getting more than one drop per second out of the VBV. Also, every time the pump turned on to pull a shot, you'd probably have the full 9 bars coming into the steam boiler which might blow the OPV on top. So this must be just the tiniest of leaks.

One test you could run when the machine is cold is to pull up the pin on top of the VBV and hold it closed for a minute or so and then let go. That way you could see if there is enough pressure building up to hold the VBV closed. If so you can then watch the steam boiler pressure gauge and see just how far the pressure builds before it levels off.

[goodboyr]

Aha! Thanks! Will give it a try.

[goodboyr]

I let it cool down, and this time it didn't leak at all. I checked the level sensor and its fine. Cleaned a bit off it, but its inserted at the right level, not loose, and was pretty clean. Not sure what happened here. Started it up again, and its working fine. Weird.