This is a cross post from Coffee Geek as I have not received any replies there to what is a technical issue. The link is here

https://www.coffeegeek.com/forums/espre ... nes/678822

I'm modifying the question slightly.

Am having a problem with an Expobar Pulser. The vacuum relief valve won't shut on its own, only if I pull up on the brass plunger. I replaced the valve with a newer model that doesn't have a plunger, it won't shut at all. Steam and drops of hot water come out, a lot of steam, but won't close.

When I close it the boiler generates pressure. But it seems extremely hot, to the point where when opening the hot water tap steam pours out, more than usual I think.

The autofill seems to be working. I replaced the pressurestat as well as the relief valve. Haven't been able to test it with a multimeter.

One fact--the machine was descaled by a service company here a couple of weeks before these problems developed. I am wondering whether a failure to properly clean the boiler might be causing some of these issues.

I'm at a loss as to why the boiler would produce steam but not close the valve. Wonder if anyone has dealt with this. Thanks

johnc wrote:I'm at a loss as to why the boiler would produce steam but not close the valve. Wonder if anyone has dealt with this. Thanks

It comes up a lot, but usually in the context of false pressure and the vacuum breaker failing to open. Even though the symptom is different (valve has failed to close), yours is very likely the same underlying cause, namely, the valve seat is either worn, defective, or the seat has scale/grit on it that prevents it from sealing properly.

Have you descaled the steam boiler lately? If not, you should do it, since a sticky vacuum breaker and a scaled steam boiler typically happen together. You could simply soak the valve in white vinegar to test my assumption that the valve is sticky, but don't neglect to descale the steam boiler. It's a lot easier to descale a lightly scaled boiler with ordinary white vinegar or a mild citric acid solution then wait until it's really bad and only lots of disassembly, tools, soaking, and harsh acids will do the job.

johnc wrote:One fact--the machine was descaled by a service company here a couple of weeks before these problems developed. I am wondering whether a failure to properly clean the boiler might be causing some of these issues.

UPDATE: Re-reading your post, I overlooked this key point. If the vacuum breaker isn't sealing, I'll stand by my original suggestion that it's either failing to close due to grit or the seal itself is defective. If you post a photo of the valve, it may help with the diagnosis.

Thank you. What puzzles me is that a brand new relief valve is also failing to seal. Perhaps the boiler needs further descaling. The descaling it received was the first ever. Yes, too long, but we have very low mineral content water so I avoided it. I will try that and post a photo or video of the results.

You mentioned that it sealed if you pulled up on the valve's pin. What's the steam boiler pressure once it closes and the pressurestat turns off? Normally it doesn't take a lot of pressure to push the pin up. If it closes and stays closed after you pulled up the pin, then there should be adequate pressure to close by itself... unless there's something preventing it from moving easily (e.g., scale, defective seal).

Good question. The Pulser does not have a pressure gauge and I've never installed one on it. So I don't know. What I do suspect is that my failure to descale the machine may be causing the problem. I didn't touch it for many years. The service company did a descaling but I am guessing that all that did was start the process of dislodging accumulated gunk which is now causing the problem, even for the brand new valve. Hopefully not, I am not up for dismantling the boiler etc. I will try some additional descaling however to see if that helps.

I should note that when the valve seals additional steam starts to come out from somewhere (I can't quite tell where yet) suggesting to me that the boiler is overheating.

Thanks for your help on this