Hi folks. I'm new, and sorry to start off with a problem, but I need some help. I have a Vibiemme Domobar Super HX manual with rotary pump, plumbed in. It's about 3 years old. I descale every 17 weeks. I descaled it this past weekend, and since the descale, the OPV or bypass (not sure what it's called) stays open continuously when the brew lever is up and water is flowing through the group head. The flow looks about the same whether I'm pulling a shot or just running water through the group head without a portafilter in place.

I tried backing the pressure off on the OPV, and that just made it worse. Even more water flowed. I cranked it up to 14 bar, and it slowed down the flow a little, but it still dumped a heavy stream of water through the bypass line into the drip tray.

Could the OPV be stuck open? Is there a way to fix that? Maybe the spring inside is worn? Time to replace or rebuild it?

Since this started right after your last descale- I would suspect it is stuck open with scale or a foreign body that has broken free. Cheapest route-I would take it apart and clean it and/or rebuild it if parts are available. Or just order a new one and be done with it.

Ixo wrote: Time to replace or rebuild it?

Yes. On some of these you can buy a rebuild kit for o-ring and plunger seal. Stefano sells one that may work. You may need to contact Stefano and/or 1st Line - make sure it's the right kit for your valve (not sure if they might use different OPV on rotary vs vibe pump.) If no kit is available, then you may need to replace if it doesn't work after dissembling and cleaning.

The valve is in the cold line between the pump and the boiler, and I'm feeding it softened water, but it was working fine right before descaling, so you might be right, kize. I will try descaling again, and if that doesn't work, disassemble the valve to inspect it and clean it.

Thanks for the link to the rebuild kit, homeburrero. I think that is right for my valve. I'll confirm that if I end up going that route.

Before going through another descaling,
Try moving the OPV screw couple of times in and out,
or open the OPV (water will come out) and check with something is stuck

That makes sense, Stefano. I'll give that a try. To open the OPV completely, do I just unscrew it all the way out? If I do that, I'll cut the power so the pump can't come on and cut the water supply since it's always under pressure.

I tried moving the bypass valve screw in and out a few times, to no avail. I removed the screw and spring. It has a little scale on it, but not much. The holes weren't blocked. Aside from the body of the valve, there weren't any other parts that I could see. That o-ring looks a bit flattened, but the valve wasn't leaking. It's just allowing too much water to get by into the bypass tube.

I noticed a constant drip of water from the group head drain valve, so I disassembled the group head mushroom, preinfusion chamber, and drain chamber and found that the infusion valve was broken. Could that affect the operation of the bypass valve? I'll post pics of the group head parts later.

Here are the OPV / Bypass valve parts.

look for the brass seat and closing gasket is left inside the valve
picture on the way

Thanks for the picture, Stefano. Besides being a lot cleaner, your valve looks a little different from mine. The rubber (silicone?) part on mine is red. I tried to get it out, but I was afraid I'd tear it.