Steam explosion after startup

[naude51]

My S1 has recently developed a habit where about 10-20 minutes after startup in the morning there is an explosion of steam coming from the region of the expansion valve, I think. it is certainly at the bottom right hand side of the machine when facing it. It then is fine for the rest of the day. On occasion it will happen twice, but then will be fine. Sometimes it won't happen at all, but it is becoming more regular now. The machine used to drip slightly from the expansion valve, but this has stopped. I am not sure if this has anything to do with it.

[chas]

It may not be the problem but certainly the first thing you want to do is readjust the expansion valve and pump pressure. That potential issue should be ruled out first.

[naude51]

Thanks for that. I have released the expansion valve slightly and it has not re-occurred but the puzzling part is that once it happened it was fine for the rest of the day.

[naude51]

I have slackened the expansion valve and the steam explosion is not as frequent. One thing I have noticed is that after pouring a shot, when I release the portafilter there is a slight "sigh" as if there is some pressure still in the portafilter. Not sure whether this should happen as I can't remember it before.

[chas]

The first thing to try for that is a good thorough backflush with Cafiza or equivalent. It sounds like some part of the 3-way mechanism is clogged.

[naude51]

I have now slackened the expansion valve, backflushed thoroughly, and I still get the occasional steam explosion once a day. Would it make sense to dismantle the expansion valve and the threeway valve (not sure if this is possible)?

[chas]

I can't see the 3-way being involved in this. The expansion valve should open a little bit as often as needed to prevent what you are seeing, so I'd start by disassembling that.

Did you just loosen it a bit or did you actually adjust it "scientifically" per these instructions: s1v2/VII_Expansion.php

[naude51]

I must admit it was not scientific, I just loosened it a bit. I will be attempting to dismantle the valve when I get a chance.

[chas]

Just an advanced warning for re-installation of the expansion valve. The expansion valve spring is very strong. You have to push up hard while turning it to get the threads to re-engage. After some trial and error I discovered that if you remove the drip tray (well, you have to do this anyway...) and put the right sized metric deep socket over the valve you get a lot better leverage. You can grab the socket and push up a lot easier than trying to get a good grip on the valve directly.

You CAN get it on without using the socket method, just be prepared for it to work you a lot harder.

Also, if you haven't scientifically adjusted it using the linked method in my previous post, try that before you disassemble the valve.