My BZ10 started leaking into the water reservoir from the tubing leading into the OPV.


Symptoms:

• When the pump is running there is a stream of water coming out of the tubing shown in the photo.

• This pauses for a moment after the pump stops, then when the boiler pressure rises I have boiling water leaking out of the same tubing.

What I've done:

• Replaced the pressurestat assembly as I assumed the problem was on that end before doing proper troubleshooting.

• Took out and cleaned & descaled the OPV (outlined in blue in the photo above).

• Disassembled and descaled the red and green parts. I couldn't really work out how to remove the solenoid plunger form the green section so left that alone.

Background:

• This began after I took out about 1 L of water from the boiler using the hot water tap (as per Bezzera usage instructions for when the machine has sat idle for a few days).

• Machine is 4.5 years old and has always been run with filtered water (BWT Bestmax) but has never been descaled in a soft water area (average of 80 mg/L CaCO3 per the water company).

• The OPV did have a bit of scale when disassembled, pretty minor but enough to convince me to do a boiler descale once the machine is up and running again.

What is likely the problem and what should I do next?

Thanks in advance.

I believe that is a valve that opens to save the pump when there is a blockage further up the water path - the OPV feeds the group and the solenoid controls filling the boiler.

Does water come out of the group when the pump is on?

Assuming the pipe TAV.04 connects to the boiler, I would guess that pressure from the boiler is leaking back through part # 1. But that's assuming that I'm correct in guessing that we're talking about water coming out through the hoses labeled 23, 25 and 26. when the machine is hot and idle.

Edit:
If the water coming out of the hose # 25 is hot, either hose 23 or 26 should also be hot telling you where the water is actually coming from.

I agree. The tube showing "TAV4" connects to the heat exchanger. Part 3 in the diagram acts as a non-return valve to prevent that hot water that is pressurized from thermal expansion flows back to the tank. My guess is that that valve is passing. I don't know if you disassembled the whole T-piece or only the part that connects to the hose that runs to the tank? You may want to disassemble and descale the whole piece and put a dab of food-safe lubricant on the seals.

I agree with those saying that that is a priming valve and that you should examine/descale/clean the check valve...
But the outlet end of that priming valve itself is a cheap little rubber knob on a spring checkvalve, too... If it's passing backward, it too has been disfigured by the hot brew-circuit water flowing backward over it, you'll want to replace that priming valve, too I expect.

Thank you all for the help troubleshooting. I will try to answer all the questions.

baldheadracing wrote:I believe that is a valve that opens to save the pump when there is a blockage further up the water path - the OPV feeds the group and the solenoid controls filling the boiler.

Which valve are you referring to, can you indicate the number?

baldheadracing wrote:Does water come out of the group when the pump is on?

No, that side of things seems to be operating ok at first glance including relieving excess pressure into the tray after a shot.

ira wrote:If the water coming out of the hose # 25 is hot, either hose 23 or 26 should also be hot telling you where the water is actually coming from.

Yes, hot water can be traced back to hose 23. Based on your suggestion I took a thermal image that I think illustrates this better than me trying to describe what's hot and cold. You can see that the OPV assembly is cold at this point.

DeGaulle wrote:I agree. The tube showing "TAV4" connects to the heat exchanger. Part 3 in the diagram acts as a non-return valve to prevent that hot water that is pressurized from thermal expansion flows back to the tank. My guess is that that valve is passing. I don't know if you disassembled the whole T-piece or only the part that connects to the hose that runs to the tank? You may want to disassemble and descale the whole piece and put a dab of food-safe lubricant on the seals.

I disassembled all the bits inside the OPV assembly labelled 11 in the diagram and cleaned with descaler. The same goes for everything else in the diagram with the exception of parts 22 and 19, which I couldn't easily undo (I did remove the solenoid valve coil #21).

Do you mean the part #3 inside the OPV? If so I think the above thermal image disproves that hypothesis as that shows hot water leaking back through boiler load hose 20 whereas the OPV is cold. Am I wrong?

JRising wrote:I agree with those saying that that is a priming valve and that you should examine/descale/clean the check valve...
But the outlet end of that priming valve itself is a cheap little rubber knob on a spring checkvalve, too... If it's passing backward, it too has been disfigured by the hot brew-circuit water flowing backward over it, you'll want to replace that priming valve, too I expect.

Sorry just to be clear, you are referring to valve 15 in the diagram and also 27? As they are both plastic I was unable to disassemble the valve for fear of breaking something.

To recap, I just ran things again and there are actually two symptoms that point to the source of the trouble:

• when turning the machine on and the pump runs momentarily to fill the boiler, cold water is being pumped out of hose 23
• once pressure starts to build in the boiler then there is hot water running through hose 23

What is the component whose job it is to prevent these things? Is it just valve 15?

Sorry this complicates it, but it is such a world... Part 3 in Valve 11 is the check valve for the brew circuit. It should prevent the hot water from that circuit from destroying the check valve in the outlet of the valve 15, priming valve. There's also the solenoid valve on the steam boiler side of that T-Fitting after the priming valve, but I think we're deciding it isn't leaking, the brew circuit is the problem.

So #15 is probably damaged, it can't handle the hot water. #11, is supposed to prevent hot water from damaging the cheap valve, but #11 needs to be inspected/cleaned etc... #15 could probably have its cheap little check valve ball replaced with the identical one out of an Ulka pump, but I'll bet that priming valve isn't expensive.

Lastly, it's ok that the priming valve lets out water when the pump is running, that's how the machine can get any air bubbles out of the system. But it's not okay that water is flowing backward through the priming valve to the reservoir.

JRising wrote:Lastly, it's ok that the priming valve lets out water when the pump is running, that's how the machine can get any air bubbles out of the system. But it's not okay that water is flowing backward through the priming valve to the reservoir.

Thank you, that makes sense.

JRising wrote: So #15 is probably damaged, it can't handle the hot water. #11, is supposed to prevent hot water from damaging the cheap valve, but #11 needs to be inspected/cleaned etc... #15 could probably have its cheap little check valve ball replaced with the identical one out of an Ulka pump, but I'll bet that priming valve isn't expensive.

I worked out how to open #15, there is a plunger-type valve in there that looks a bit worn and won't be able to make a seal. The interesting part is that the plastic valve has been discontinued and replaced with a metallic version, which I will now be using instead as a replacement.

JRising wrote:#15 could probably have its cheap little check valve ball replaced with the identical one out of an Ulka pump, but I'll bet that priming valve isn't expensive.

Spot on! Thanks for this tip, I did as you say and cannibalised a spare Ulka pump that I had included in my last order (the cost of the pump is basically less than the shipping cost) and that resolved the leak! It's been running all afternoon and I'm about to put it back into service. Will swap out the valve when I get the replacement part or perhaps if I am able to purchase the valve alone to put in the Ulka I might go down that path instead.

Many thanks to all who contributed in finding the solution, I really couldn't have hoped for a better response than I got.

Good stuff. That valve tip is visibly out of shape.

But did you inspect the other check valve, all the internals of part 11? If that check valve is still allowing full expansion valve pressure to continually press hot water backward toward that little priming valve it will probably be able to kill your replacement tip in short time.