Hi All,
So, I did a full descale a few weeks ago including pulling the mushroom out of the group. All was fine for the first week but then over the last week my machine hasn't been able to maintain stable group temperature over long periods of time.

I'm using Eric's grouphead thermometer adapter which usually shows a stable group temp of about 208F. If my machine sits for more than a few hours, it will drop down to 160F or so. If I flush for a few seconds, it will usually rise up to above 200F or more after a while only to drop again after a few hours.

Any ideas guys on how to fix this? Is there some kind of blockage in the thermosyphon? An air bubble? Is it possible that water is slowly leaking out of the bottom of the group from the plunger below the mushroom? I took the autofill rod out to check the condition and everything seemed fine. I even raised it by a couple of mm's in case the boiler water level is low for some reason. Thanks,
Kaelin

a stall can happen if you flush a little water after a shot to clean the screen. If you do a plain water back flush, you should have no trouble.

If your routine is the same as before descale, then you may have a blockage in the flow restrictor

After the group has cooled (to 160F or so), how long does it take the water to come out of the group when you flush for a few seconds? Is this longer than normal? If so, it is very likely that a seal is letting by, either in the group or the OPV, allowing the HX to partially run dry and stall the thermosyphon. If the water takes the same time to leave the group (almost immediately) after a long idle time, then it could be a partially blocked thermosyphon - as cafeIKE says the flow restrictor.

Hope this helps,

Martin

Thanks Ian,
My routine is exactly the same as before and I am familar with the odd stall that is easily fixed with a 4 second flush or so. This morning the group was at 160F. When I flush it in a "stalled" state, it sounds strange, as if the group is filling with water again.
If there is a blockage in the restrictor, how would I remedy it?
Cheers,
Kaelin

Mole wrote:After the group has cooled (to 160F or so), how long does it take the water to come out of the group when you flush for a few seconds? Is this longer than normal? If so, it is very likely that a seal is letting by, either in the group or the OPV, allowing the HX to partially run dry and stall the thermosyphon. If the water takes the same time to leave the group (almost immediately) after a long idle time, then it could be a partially blocked thermosyphon - as cafeIKE says the flow restrictor.

Hope this helps,

Martin

Hi Martin, just caught your post after my last. But yes, it seems like the water is taking at least twice as long to appear out of the group. If the HX tube (brew water) was not filled with water, would that make a difference for the temp of the group? My understanding was that the thermosyphon is fed from boiler water, and failure of water to circulate through it would contribute more so to low group temps. (I am far from an expert at this stuff)
Cheers
Kaelin

The thermosyphon will be taken from the HX not the boiler. There will only be two pipes going to the group, one coming in from near the top of the HX, the other going to nearer the bottom of the HX. Then, the pump inlet to the HX will probably be at the very bottom of the HX. If the HX is allowed to run partially dry, so that some air/steam builds up at the top, as the water level reduces and passes the level of the outlet pipe to the group (inlet of the thermosyphon loop) it will prevent water flowing and the thermosyphon stalls. You flush the group, which takes longer than normal for water to flow as it must refill the partially emptied HX, and then the thermosyphon starts again, heating the group for a few minutes, until it begins to run dry again and stalls.

So, assuming there is only one problem, it is (probably) that the HX is running dry (at least partially). There can really be only two places this is happening. Either the OPV is leaking: this can be checked by observing the OPV return pipe to the tank (or drip tray, or wherever it heads to) - a steady dripping from this pipe over a few minutes to hours after the last "flush" will show that it is letting by. Alternatively, hold the pipe and shake some water out of it, then hold it upright (so the end is higher) and see if the water level raises in the pipe over time. Is it a rotary or vibe pump machine? If a vibe pump, when you descale, do you do a blind backflush to clear out the OPV with descaler solution? You could try this to clear the OPV, letting it sit a minute or two between backflushes. Alternatively, the OPV is normally easy to take apart and descale outside the machine.

Secondly, the seals in the group could be letting by. I'm not sure of the best way to check for this. You could try another (fairly aggressive) descale of the HX circuit only (come to think of it, you are descaling the HX circuit and boiler as part of your descale operation?). It could be a lump of scale trapped in a seal somewhere.

The only other thing could be a leak somewhere in the HX circuit within the machine. Inspecting the pipes and joints throughout the machine for leaks (or scale buildup which would indicate a leak) would rule this out (probably!).

Hope this helps,

Martin

buzzmccowan wrote:........but then over the last week my machine hasn't been able to maintain stable group temperature over long periods of time.

When this thermo-stall was first reported here about a year ago I wondered, but I didn't have to wonder long because it was a week or two later that it happened to mine. iirc, Dan thought it odd, and just after reported it, the same thing happened to him.

Since that first time, it has happened two subsequent times. Once it takes place I have to flush a lot of water, wait, repeat, and do that a few times to get it back up to temperature. Every time it has happened it has been after the machine has sat idling for a long period of time (I will guess three to five hours).

There has been discussion of the scientific reasons it happens here on HB (or at least theories mentioned) but I don't think that your cleaning regime had anything do do with it other than coincidence.

thanks Martin and Randy,
I plan on spending some time this weekend trying to figure it out. I've had the odd stall over the last year but there is a consistent problem every time the machine sits for more than a 3 or 4 hours now. I'll report back what I've found. Thanks. Kaelin

Pull out the mushroom. Do you see tiny sparkly bits in the water?

Descaling removes pieces of the chrome plating on the interior of the E-61 brewhead, and then they migrate to annoying locations where they clog the flow. I had to put mine through a thorough cleaning, including removing all the remaining interior chrome, to get it to work properly again.

Assuming the boiler remains at temperature, there is only one reason the group gets cold : NO Flow.

There are two possibilities for No Flow :

Blockage
Vapor Lock

Blockage seems unlikely in this case as evidenced by the change in water discharge when cool.

Which leaves Vapor Lock.
Review the images in E61 Group Espresso Machine: Detailed Interior Schematics Brew Path Close-up and anotated

Assuming none of the mechanical HX connections began leaking after descale, it can only be one of a few places

Brew Valve
Upper Group Sleeve Chamber Seal
OPV
1-way Valve back through pump

As the first two items were disturbed, check there first.
- If the Brew seal is leaking, water should drip from the bottom of the group. After brewing a shot, remove the drip tray, wipe the whole bottom of the group dry and see if an ever increasing puddle collects over the next hour.

- If the Upper HX chamber seal is leaking, water may be visible on an extended blind filter run. Run the pump for a full minute and check for the tiniest drop around the seals. This may also help flush the OPV.