Hello all, I've been stalking this forum for a long time now and figured that if I am going to benefit from all of the great experience in this community, then I should be active in the discussions. So here goes my problem.

I bought a used and very neglected Isomac Millenium for (what I hope was) pretty cheap. I disassembled and found it completely full of calcium deposits. After lots of cleaning, replacing the pump, opv, and rebuilding the grouphead with new valves, springs, and gaskets, I was ready to start it up.

Starts up fine, pump sounds strong, fills the boiler correctly. After 30 min or so I checked on it, boiler pressure at 1.3 bar. Steam output is virtually never ending (compared to my gaggia classic) hot water works. Problem is when I lift the lever to brew, it seems like it takes forever for water to come out. I tried a shot with fresh locally roasted beans with the same grind settings as my gaggia. It totally choked the machine. 30+ seconds for an 8g single. Adjusted the grind and after several more attempts, I got a 22 second single, using almost pourover consistency grind.

Anything I could've done wrong assembling the grouphead? I'm a BMW Master Technician, so pretty technically adept, not sure what's wrong. Apologies in advance by the way in case this is the wrong section for this post, or if it is too long. This is my first post on any forum, so not sure the protocol. Thanks!

//Mtech wrote:Problem is when I lift the lever to brew, it seems like it takes forever for water to come out.

Since you've just descaled, I'll assume there's no blockage at fault and instead suggest it's a thermosyphon stall. That happens when air is allowed to enter into the thermosyphon loop through either a drip drip drip of the E61 brew valve or an expansion valve that's failing to close. The key symptom is that the delay only occurs if the machine has been idle for awhile, i.e., there's no delay after the first one if pulling back-to-back shots.

Randy's article Understanding and Preventing Thermosyphon Stall explains this problem very clearly.

I don't believe there is any blockage. I had the group disassembled but installed in the machine and it seems like I get alot of water through the lines then. Thank you for the reference material, it was great information. My issue sounds similar to a thermosyphon stall, but, as recommended in the article, a long flush does not really fix it. Once all the steam is purged out it gets a little better. I realize I have no HX experience, having only used a gaggia classic before this, but from watching YouTube videos of cooling flushes, other users are getting what looks like twice the water flow. I will disassemble in the morning, maybe a valve is hanging up in the grouphead. Thank you for your response.

Did some diagnosis this evening. Pulled apart the cam lever to actuate the valves. Today, no water came through the brew valve. With it hot and pressurized, I cracked open the mushroom valve and steam and water spewed everywhere, still no water through the valve. Turns out the flow restrictor (assuming that's what the small holes in the mushroom valve are for) was plugged up. A needle fixed the problem. Runs like a champ now! Just need to practice cooling flushes. I'm using a fluke, so should be ok. Thanks again for the help, even though it was my fault for not paying attention to detail while having it disassembled.

Thanks for the update, glad to hear it is working again.