Odd Expobar problem - no thermosiphon

[CrackAddict]

My Expobar Office Control worked flawlessly for several months. When I first received it, pressure was at 14 bar, so I cranked that down (turning the white nylon screw in the valve counterclockwise) and also took the opportunity to route the (increased) bypass overflow back to the tank, as I use $$ Volvic water to reduce scaling in this high-scale area. Note the pressure on this machine must be checked using a PF gauge as there is no integral gauge.

As mentioned, all was fine for several months and machine would be up to temp from preheating on a timer in the AM. Then, one day, machine is much cooler. Grouphead only warm. Actuating vibe pump results in no flow for +20 seconds, then a tone change and pumping commences. Machine then warms up normally, but not ready to go for 20 minutes or so.

I rechecked all internal componets for leaks, etc. Vacuum break works correctly. No air or water leaks. Powering up without covers and then powering off after one hour, I noted the top pipe from the HX coil to grouphead is HOT, while the bottom (return) pipe is COLD, so NO thermosiphon effect even though boiler is HOT. Actuating the vibe pump manually seems to initiate thermosiphon, but the "passive" start has stopped working. ??? I disassembled the top of the group head (large brass plug). No scale. Small circular screen and orifice - both clean.

Once warm, this machine works fine - but I cannot figure out what happened to the "preheat" phase. On a practical note, this "costs" me a few minutes each morning as the machine requires intervention to achieve a ready state. I also replaced the Ulka pump - just on a long shot and because it was easy. No effect.

I have discussed this with the dealer - who considers it not a "fault" since the machine still makes great coffee. I have also asked the importer and other experienced people and all seem at a loss to explain the problem. Help!

[HB]

Actuating vibe pump results in no flow for +20 seconds, then a tone change and pumping commences. Machine then warms up normally, but not ready to go for 20 minutes or so.

Do you mean that without coffee or a blind basket, the flow takes +20 seconds and the pump tone changes (indicating it's under load)? If so, then you need to find out why the line from the pump to the group through the heat exchanger is partially blocked. The heat exchanger is part of the thermosyphon loop, so blockage there would explain why the lower return is cold. My first thought is scale build-up. BTW, twenty minutes or more to heat up is "normal" for heavy group machines like the Expobar.

For reference, the picture below is the boiler of an Expobar Lever. I think it looks similar to yours.

[cannonfodder]

Sounds like air-lock. What position do you leave the lever in? Should be down when heating.

[CrackAddict]

Wow! Thanks for the replies.

This is the Office Control, so it is solenoid-actuated - not lever. The internals are similar to the posted photo, however. I would imagine the grouphead is similar but with the valve actuated by the solenoid. The delay in vibe pump water delivery is only for the first pump of the day. If the machine remains on, water delivery is normal after this first delay. So if it's a blockage, it's a strange one.

I do not think scale is the problem, as the machine was only used with Volvic water from new, and in addition I have a resin filter in the tank. The machine was brand new when I received it (still had the gummy plastic on the panels) but had been new/old stock (manufactured in 2001). It worked perfectly for about the first month. The machine is on a timer, so it comes on about an hour before I wake up. Normally, that would be plenty of time - I could do a purge and pull a shot immediately.

Now, the grouphead is so cold when I get up I can rest my fingers on it. The top of the machine is warm, though - about 100F - and there is plenty of steam in the boiler. So the boiler is hot, but the HX is not circulating. Operating the vibe pump seems to get this flow going - I assume it is injecting cold water into the HX coil at the bottom, and this either jumpstarts the thermosiphon or physically circulates the water through the grouphead (I am uncertain). As I mentioned, there was no scale in the top of the grouphead when I investigated. Neither was there any scale on the vacuum break.

While I suppose some rogue scale or foreign object could have migrated over a month into a location where it partly plugs the HX loop, why then does the machine not cool off again after use? Once I have "kickstarted" the thermosiphon using the vibe pump, it stays hot all day. It only stops thermosiphoning after an fully-cooled off cycle.

I notice that often when repowered on during the day, the machine will actuate the vibe pump immediately. That is, on power-on, the vibe pump runs immediately for about five seconds. When the machine is well and truly cold (as in morning startup from overnight), the vibe pump does NOT run. I wonder if - rather than a hardware problem - this is a software/sensor control problem in that the "kickstart" for the thermosiphon is the brief vibe pump action upon startup that is not happening?

I realize the vibe pump actuation is also filling the boiler and this is not always called for. But I wonder if it should *always* kick in the vibe pump at startup, and for some reason it has stopped doing this? perhaps a bad thermostat?

Sometimes it's easier when things are just broken!

Finally - the Expobar in the photo has the insulation nicely wrapped around the boiler. Is that standard issue? Mine came with just small sheet of insulation between the boiler and tank. I would like to add some as in the photo but have yet to find a suitable sheet to use.

Many thanks!

[HB]

I think Dave is on to something. I remember a number of reports of Expobar pumps "losing prime", although that shouldn't affect on the thermosyphon. My quick read of the search results on CG weren't very illuminating. To make certain we're all on the same page, below is a schematic excerpted from How I Stopped Worring and Learned to Love HXs:


HX thermosyphon

I suggested scale buildup as a possibility because the HX is a big section of the thermosyphon loop. Now that you mentioned that resin water softener, I suggest removing it at least temporarily as they are well known for clogging.

Finally - the Expobar in the photo has the insulation nicely wrapped around the boiler. Is that standard issue? Mine came with just small sheet of insulation between the boiler and tank. I would like to add some as in the photo but have yet to find a suitable sheet to use.

Abe's Suggested Upgrades in the Brewtus Buyer's Guide Epilogue recommends foil-backed insulation (the Expobar Brewtus has the same stock insulation as the Lever pictured earlier).

[CrackAddict]

More thanks. I have checked the resin filter - no clogging. I use two and recharge them alternatively.

I have never seen a cut-open HX boiler (might be nice to) but I expect the innards contain a large coil of tubing that forms the actual heat exchanger. Since I have hot water in the exit (top) pipe, any blockage is likely to be in the grouphead itself or in the bottom of the boiler.

I guess my options are to first try descaling (easy, even though I doubt that is it) or disassemble the entire system to find the problem. I wonder if it is possible for the three-way valve that injects water into the HX to be faulty? This might explain the lack of pumping on a cold start (valve sticking). The EX-5 pump itself is fine (I swapped it for a new one). If the valve was sticking in a part-way position, I am assuming it would pump water into the boiler at the same time as the HX, correct. That is, this valve (at the base of the boiler/HX and in line from the pump) supplies water *either* to the boiler (as demanded by a level sensor or pressurestat of some sort?) OR to the HX. So if it was leaking or had some debris in it, it might try and pump water to the boiler when it should be pumping to the HX. Worse, if it remains "open", it might allow the thermosiphon to "short-circuit"?

The simplified schematics, while very helpful, don't quite get to the level of detail needed to sort a problem like this. Do anyone have a detailed diagram of the valve in question?

The other possible clog point is in the base of the grouphead. I see the lever machines have a "mushroom" that is mechanically controlled, whereas this machine has a solenoid, but I suspect the operation is similar, and that it is relatively straightforward to disassemble the water flow controls in the grouphead?

Thanks very much for the link to the Brewtus group - many resources there!

[cannonfodder]

Over on CG EN had a similar problem with his Millennium. After 6 pages of ideas and trials it turned out to be an air lock in the pump. Here is the thread, you may want to give it a look and see if anything works for you. I believe his GH was heating though; it was just the pump that had a problem (brew and boiler fill).

[lennoncs]

Check the solenoid valve that diverts water to the boiler.
if that valve is leaky the HX water can settle back into the boiler when the machine cools.
a faulty vacuum break will suck that water out of the group if the valve is leaky also.

the night before,

Get everything running well, get a measuring cup and measure how much water you get from the water wand before the re-fill kicks in.


the next morning,

when the machine is hot but the group is still cold(malfunctioning) do the water draw and see if you get more water before the refill kicks in, that will tell you if it is backing into the steam boiler.

also;
do a level check on the reservior to see if there is any extra water in there also.


if the group is cold...there is no water in it.

if there is no water in the group...it went somewhere.


we need to find that somewhere.


Cheers
Sean

[barry]

is there a check valve on the cold water in line, between the pump and the water distribution block? it sounds like it might be stuck open.

[lennoncs]

is there a check valve on the cold water in line, between the pump and the water distribution block? it sounds like it might be stuck open.

The OPV that expobar uses on the machine includes a check valve on the input (pump), it is screwed into the outlet of the pump.

Here is a document on the OPV.


Sean

[CrackAddict]

My money is on the three-way solenoid valve. The OPV example is very similar to mine (I don't have the "anti-aeration" line) but it is downstream from the 3WSV, so if that was functioning correctly, there would be no pressure back against the OPV.

If there is dirt or a defect in the 3WSV, though, it will leave the boiler and HX coil "connected" and perhaps cause my problem. It could also help explain the long "run up" in the pump pressure in the morning.

I've contacted the distributor to check on spares, as I'd rather do a quick parts swap than have the machine down for any time (OK - I'm addicted!). Once I have a new OPV and 3WSV, I will report back on the effects of the swap and any other findings. In the meantime, I will try the suggested water replenishment timing, but I suspect this is not very repeatable. Since it's a HX machine, the pump can either supply water to the grouphead OR replenish the tank (depending on the position of the aforementioned 3WSV).

If my understanding is correct, you can empty the reservoir "making coffe" as the pump is busy pushing water through the grouphead. It is only *after* the solenoid closes off the HX that the signal to feed the boiler is actioned.

Or I am confused? - thanks for all the suggestions

BTW - as a bit of introduction - I'm a Canadian, married to an American, living in London, UK. As my interest in coffee has grown, I have scaled (no pun intended) my equipment up, but I feel a bit restricted by the knowledge that some day I will move back to the US or Canada and all this 220/240V, 50 Hz equipment will be on eBay. I settled for the Expobar Office Control as it was a very good price in the normally overpriced UK market. (Think same number in GBP as in US$ - about 80% more... for a product made closer to home.)

Perhaps in retrospect, I should have gone with a non-electronic (i.e. lever) controlled machine as it's relatively simple to provide 220V power in a US/CDN residence (like an electric dryer) and only the pump in a lever machine is likely to need to be changed for the North American 60Hz supply. I know - another thread, another time!

[CrackAddict]

BTW - it would certainly be handy to see all the pipes in this picture labeled - I don't see that degree of detail in the Brewtus website (yet).

I see the large upper and lower HX pipes. The large pipe/fitting in the center of the boiler bottom must be the HX feed, as it is "in the loop" from the grouphead.. Then one of the pipes (at the bottom) must be boiler water in? (which one?) The plastic line on the right must be the water feed from the reservoir.

That leaves one medium size copper pipe in the bottom of the boiler, and one small and one medium pipe running from above the grouphead - the small one to the something on top of the boiler, the medium one to something out of sight below the boiler. Can anyone identify their functions? Oh - there is yet another medium copper pipe visible between the upper and lower HX pipes - it seems to be snaking out into the background - perhaps to a pressure gauge? (The Office has no gauge.)

Thanks!

For reference, the picture below is the boiler of an Expobar Lever. I think it looks similar to yours.

[lennoncs]

Hi CrackAddict
Yeah, I have a very detailed rundown of the piping in the Brewtus, I am just too lazy to post it and no one has asked.

The test I am talking about regarding water volume is done with the water wand not the group and the volume is measured when the pump to refill the boiler first goes on. the purpose is just to see where the water is going. the most likely candidate is the valve under the boiler.

sean

[CrackAddict]

Thanks ever so much for the pipe ID - very helpful!

Also my apologies for misreading the suggestion on timing water flow to refill. I have just checked with a hot (ready) how much water I can get from the hot water (tea) tap before the pump kicks in and it is almost nothing - less than 25 ml. Any use of the tap essentially results in an almost-instant triggering of the pump to refill the boiler. I will follow up with the cold machine results asap.

[lennoncs]

you are most welcome.

No worries,
it was difficult concept for me to put into text and lost a lot in the translation.

let us know what the final result is

cheers,
sean

[CrackAddict]

Test results are in and on a cold startup, the tea tap provides about 75 ml of water before the refill kicks in. While not much, this is more than 3X as much as when hot and "primed", when almost any use of the tea tap - even a few drops - will activate the refill.

This doesn't seem like a large amount, but perhaps it is enough to show that the 3W solenoid valve is leaking?

I have contacted the distributor to see if I can get a new valve at a reasonable cost. It's as easy to replace it as try and fix. If the replacement solves the problem and I can clean the original, I'll have a spare.

Will keep you posted.

[lennoncs]

Looks like you found the culprit. probably a piece of junk in the valve seat.

I would check the vacuum break on top of the boiler just to be sure it is not sticking and speeding the process along.

good luck!


Sean

[Skealoha]

Does a plugged Over Pressure Valve also create vapor lock situations? I have problems that are identical to what CrackAddict described with the difference being that I have an Expobar Lever. I noticed that the unit comes up to pressure very quickly sometimes and there is no heat to the group head. I have to take the top lid off and slightly push the metal shield covering the boiler to relieve the pressure. The pressure will then come up normally and the unit will start heating fine. I thought it was due to the clearance of the vacuum relief valve from the top metal piece (it seems like it's about 2mm or less).

Also was getting what I thought was excessive dripping to the overflow pan so I turned the OPV screw down two turns. Should I have done this?

Thanks for any ideas. The info on this thread has been a huge help so far.

Scott

[CrackAddict]

I'm not sure what you mean by "slightly push the metal shield covering the boiler". Can you be more specific? Turning down the OPV valve lowers the pressure to the grouphead and - on my Office Control at least - increases the "dump" water into the drain pan. This is because the Office is set up to just dump any excess water flow diverted by the OPV valve. I used some aquarium tubing to route this back into the reservoir. Note: put a loop in the line at the top if you do this to prevent any possibility of siphoning back.

I still have the same problem. I took apart the water control solenoid (which is actually a two-way valve) and cleaned it to no avail. I have a new one now but have not tried to put it in yet. Expobar used a larger 1/4" valve on these machines so it was hard to come by.

Tell me - does your machine take a long time to "pump up" in the morning when you turn it on? By that I mean does the water pump run for 20+ seconds on power-up?

[Skealoha]

CrackAddict,

I was referring to the vacuum breaker valve on the top of the boiler. When I push the metal piece that sits over the boiler (and is just above the valve) I am able to bleed off the pressure from the boiler. There's enough flex that it doesn't permanently bend out of shape and there's minimal clearance between the stem of the valve and the plate. For some reason, the unit's been coming up to pressure normally this week without me having to do that. I've considered calling Chris' Coffee to find out about the vacuum breaker valve replacement he sells which he claims will get rid of the vapor lock issue.

No. I don't have the "pump up" issues you have described, but more the issue where it takes the water about 20 seconds or more to start coming out the nozzle. As one of the previous postings noted it's as if the system has "lost its prime."

I'm going to try working cleaning out the OPV this evening, but now I'm sure the pressure will be out of whack. I'll have to count the turns on the screw I guess. Another $51.00 and I can buy the pressure gauge/portafilter from Chris's Coffee too !

Thanks for the tip on routing the water back to the reservoir. I might give that a try.

Scott