Expobar Office Lever - Thermosiphon puzzlement

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MarkMcC
Posts: 2
Joined: 3 years ago

#1: Post by MarkMcC »

Greetings,
I have a single boiler, HX - E61 machine with a thermosiphon that's running Cold at the grouphead. This one's got me stymied! Many posts I see regarding these types of machines complain about the group being Overheated, and requiring a "cooling flush" prior to pulling a shot. Some have resolved this problem by inserting a restrictor in the thermosiphon loop to slow the convective flow of hot HX water through grouphead.
My machine was hitting a thermal equilibrium at the grouphead of only about 140 degrees after warmup. Pulling a shot will get my grouphead thermometer up to maybe 160 degrees, but then starts to lower again as cool water is forced through the HX. Anyway, pitifully cold :cry: Here are the things I have done so far to try and understand / rectify this problem:
Descaled the HX.
Descaled the boiler.
Replaced all three valve assemblies in the E61 (they needed it anyway)
Examined the upper thermosiphon tube from HX to E61. The tube is clear, and showed minimal scaling.
While this tube was removed, I also REMOVED THE RESTRICTOR in the upper thermosiphon tube at HX port.

After performing these steps, my equilibrium temperature is now up to about 175 degrees. Still well short of 200-ish. I think I can probably attribute this improvement to the removal of the restrictor, but I'm not sure. The descaling didn't seem to loosen any horrors of build up, so I don't think that contributed much if any of the improvement. Side note: boiler seems fine. The pstat is set to (and achieving) around 1.2 bar and steam and hot water spigot are both delivering.
So, what the heck is going on here? The boiler is running good and hot, and after descaling and removing restrictor, I would think the thermosiphon loop is clear. What else can I do, and where else can I look? What else could be impeading the thermosiphon :?:

Oh, one final note. Prior to any of the actions taken above, I discovered that I can get the grouphead over 200 degrees by putting the lever in the pre-infusion position for several seconds. Hot water and steam pass from the HX (not sure through which port) up and Through the grouphead, dribbling out at the portafilter screen. So this is a pass-through, not a closed loop.

Any thoughts you might have on this, I'd love to hear them .... :mrgreen:
Cheers,
Mark

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ira
Team HB
Posts: 5497
Joined: 16 years ago

#2: Post by ira »

You can search for "thermosyphon stall" to find some suitable threads. As I recall it's commonly air in the thermosyphon loop, but I'm working from old memories.

Ira

NicoNYC
Posts: 180
Joined: 3 years ago

#3: Post by NicoNYC »

I recently rebuilt my Office Pulser, which I think has the same boiler, tubing, and grouphead, just with an electric solenoid rather than manual lever. It had the same ridiculously low idle temperature, even with the boiler at a good pressure.

I found was that the thermosiphon return (from the lower port on the head to the bottom of the HX in the boiler) was scaled quite badly, to the point that water couldn't even pass, particularly at the 90° bend as the pipe turns to go up the side of the boiler. Pulling just that tube out is pretty easy, just takes some good leverage to break those fittings.

Now my machine is set to barely over 1 bar, with the restrictor plate in place, and I find it pulls about 210 from idle, 200 after flushing.
LMWDP #718

MarkMcC (original poster)
Posts: 2
Joined: 3 years ago

#4: Post by MarkMcC (original poster) »

Thanks. I will see if I can pull that tube too. The top one wasn't too hard to do.
One other experiment I tried prior to removing the restrictor was to see if I had water flow through both the ports at the E61 when running the pump. I removed the the mushroom and (while machine was COLD!) tried covering the ports in the E61 one at a time with the tip of my finger.
What I found is water flowed freely from the lower pipe but slowly through the top one. This led me to pulling top pipe and restrictor. Palpable pump pressure was felt at the lower port but not at the upper. This, and the free flow of water through the lower port, leads me to think the lower pipe is clear. I will certainly take your experience under advisement and pull that tube next time I open her up though. Thank you :D