# Expobar Dual Boiler - thermosyphon and PID



## itguy (Jun 26, 2015)

Hi Everyone

I've got a Expobar Dual Boiler (Brewtus IV) and have recently started having a few problems with it (I don't think these are connected btw, just coincidence).

1. The PID seems to overheat and switch off. If I run the machine without the case on everything is fine, but assembled as it should be, after about an hour of warm up the PID goes blank and then won't come back on until the machine has cooled down. Seems odd that it would just give up after a period of time though?!

2. The thermosyphon system for the E61 seems temperamental. Sometimes it seems to work correctly (ie machine on for 30 mins and grouphead nice and warm), but other times, same conditions, grouphead barely warm. This was happening before the PID issues and is the same if I run the machine with the case off (ie the PID working fine).

I looked for loose connections on the PID etc but all seemed just fine.

I've dropped it off at Bella Barista yesterday for them to have it for a week or two to investigate as I didn't really want to start randomly pulling pipes out of it etc.

Any ideas or thoughts as to that these issues might be?

I read somewhere about the boiler water level in the brew boiler being critical to the thermosyphon working correctly, but I can't see a way of changing that on the Expobar as it doesn't have a level sensor and is basically run 'full'? Unless it's dropping some water out overnight somewhere/somehow? There are no leaks out of the machine.

Thanks


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## bronc (Dec 10, 2012)

Your second issue sounds like a thermosyphon stall: http://www.frcndigital.com/coffee/stall.html


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## itguy (Jun 26, 2015)

Interesting read. How do I try and cure that though? There isn't that much to wear out in the expobar, so would a faulty opv or vac valve on the steam boiler have an effect?? It's like the water level in the brew boiler is dropping slightly overnight when the machine cools down and then it leaves the slight airlock at the top grouphead pipe.


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## bronc (Dec 10, 2012)

How old is the machine? What water do you use? It could be scale related.


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## itguy (Jun 26, 2015)

It's a 2010 and I use it plumbed in with a Britta in-line filter. I deacaled it about 3 months ago with citric acid. It did this before then too. Didn't really change anything.


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## Rob1 (Apr 9, 2015)

Your second issue is due to the design of the machine. The thermosyphon goes from the top of the boiler into the group rather than from the middle, the result is when the water level in the boiler drops the thermosyphon empties and becomes inactive, this happens when the steam boiler refills. If I remember correctly the pump delivers water through a HX in the steam boiler into the brew boiler and when the steam boiler needs filling the solenoid switches causing the level in the HX to drop and thus the brew boiler level to drop and stall the thermosyphon. In my case this can happen about half an hour to an hour after steaming milk as the water level drops as the boiler cools and triggers the refill. Lifting the brew boiler until water leaves the group gets things back to normal. It's an annoying problem that happens by design.

Maybe your steam boiler is leaking, possibly through the vacuum breaker? Is your PID the old red one?


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## itguy (Jun 26, 2015)

Thanks, interesting stuff. I was pretty sure that I get the issue when the boiler switches on from cold but when the pump has not run (ie the level was deemed ok in the steam boiler). The thermosyphon then starts working ok when the pump HAS run for one reason or another (ie boiler refill or pulled a shot/flushed the brewhead).

The PID is the blue one, so the newer I think?


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## bronc (Dec 10, 2012)

The thermosyphon is passive and not related to the pump. It happens due to the different tempeture in the HX and grouphead. https://en.wikipedia.org/wiki/Thermosiphon


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## itguy (Jun 26, 2015)

Oh I understand that, but I wonder if I am having the stalling issue and then the pump running effectively tops up the water level which then eliminates the stalling?


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