My first post, though I've done a fair bit of reading and learned a lot on this site. I have a new to me Expobar Pulser that is acting up. I bought it used about three months ago and it appeared to be in good shape- very clean. It took me a little getting used to, coming from a Gaggia New Baby that I'd had for a year or so, but I think I'm getting it.

About two weeks ago, I noticed that after letting it heat up for the usual 20 minutes or so, it would sometimes take about 20-25 seconds for water to flush through the group head. Before, the water would start to run within 10 seconds or less. Then after pulling a shot, the water would be there, right away, as expected for the next shot. But if I left the machine alone for a three minutes or more and came back to pull another shot (or run a cooling flush), the pump would run for a while, and then change tone (as it reprimed) and then the water would flow through the group head.

Curious, I pulled the top off so I could see what was going on with the pick up hose. That side seemed to be perfectly fine. However, I noticed that about three minutes after pulling a shot, water would start to drain out the OPV return hose eventually emptying it. I then noticed that the water coming through the hose was boiling hot. So it seems that after a point, the HX brew water is emptying back through the OPV and into the reservoir through the OPV return hose.

Today I double checked all that with the return hose out of the reservoir, draining into a jar. It dripped water steadily as the machine heated up. I flipped the brew switch on and flushed some water through the GH and it stopped, but started dripping as soon as I flipped the switch off. When the machine was hot enough, I ran a shot (after running for 30 sec to reprime) and the water that came out the return hose switched to being cold (as it should be, right?) as the OPV valve did its work. Then, the water stopped dripping from the hose. About three minutes later, the water started to flow through the hose again, super hot, and kept going until the hose was emptied.

I've seen a couple of other threads that sort of dance around a similar symptom, but none that seem to resolve it. Am I missing something? Anyone have a suggestion for which part is failing and what I should look at? It almost seems like a valve is getting stuck open. Seems like there ought to be a check valve in that side of the system, but I don't see anything in the schematics I've seen. Any help will be most appreciated.

Your check valve is leaking. See this or other parts diagrams in the downloads section.

/downloads/ ... iagram.pdf

Thanks for the reply. I had the schematic, but with the parts all labeled in Spanish, I couldn't find anything that might be a check valve. There was an English version in the downloads area. Is the check valve in the piece between the pump and the OPV- the anti-aeration valve? Seems like that would be the right place to put one.

I could not find a separate check valve either. It was late at night when I initially responded and did not bother to look through the linked pdf.

The anti-aeration valve does have a check valve in the discharge but so does the OPV. So, I would say that the OPV check valve has failed and replacing the OPV should solve the problem or PERHAPS disassembly and soaking in white vinegar for 45-60 minutes.

I think you were on the right track. Before I started taking things apart, I ran some citric acid solution through the HX side of the system to see if that would help and it did. The check valve (whichever one failed) seems to be holding now. I think I'll wait for another failure before I go in and take the machine apart. As much as I like that stuff, with twin three-year-olds running around the house, I always seem to get interrupted and distracted if I embark on a project like that, which inevitably leads to new problems emerging. I'll wait until I have no choice.
Thanks for your help.