Thread: BZ99 boiler overfilling

Sounds like the way the machine switches from boiler to group head water flow is a issue.
Is there a solenoid for boiler fill, and another for group head flow? Or is there only one solenoid? Maybe it's leaking, or the boiler fill one is hanging open, allowing water to flow there whenever the pump is on...

Welcome Esende to CS....hell of a 1st post issue to overcome!
The Bezzera bZ99 is a HX so the Boiler and HX tube are 2 different cycles thst the water tank / pump supply.

Could it be that there is a cross over in the supply lines into the Boiler / HX Tube?

This model has a return water line to the Water Tank. Which is easily identified.
And cover's excessive water flow during over pressure / water flow to the pump during the brew cycle.
Is that still occurring?

It may be as Jack above suggested that -
There could be some moisture effected the elect connections?
Or the water level probe / connections need cleaning / checking.

GL with it.

PS search / look up the sites knowledge base on -
- Water Filters.
- TC / Talk Coffee - why he would often recommend against de-scaling!

Thanks Jackster/Espresso Adventurer,

Very helpful suggestions. Pulled both probes out today, both relatively clean. If I had inadvertently switched the terminals on the two probes, could that be causing the types of problems I’m having? I’ve checked the wires against another BZ99 (a mate has the same machine) and I believe I’ve got it correct; unless the solid vs striped wire varies from model to model?

From both of your comments, it seems most likely to me that I may have some moisture in my solenoid connections, it dumped a tonne of water out the top of the boiler. Might hit it for a little while with a hair dryer and see what happens. If that’s not it, any tips on diagnosing a faulty solenoid valve?

Thanks again for your comments gents

There is a resource on the main page of this section - 'pointy end' machines.
should show that models parts / wiring diagram

Be careful around electrickery.
I always use a safety switch / power bank between the machine and the power point.
As well as the house's power board safety switch which is hardwired / installed.

And Yes I am Irish .....to be sure to be sure to be sure !

Originally Posted by Jackster

Sounds like the way the machine switches from boiler to group head water flow is a issue.
Is there a solenoid for boiler fill, and another for group head flow? Or is there only one solenoid? Maybe it's leaking, or the boiler fill one is hanging open, allowing water to flow there whenever the pump is on...

Hi Jackster, only one solenoid, a 3 way. After tinkering a little more tonight and confirming that water on connections doesn’t seem to be the problem, I guess the next step is to pull out the solenoid valve and take a look over it. When I was descaling, I did finish the clean with a couple a backflushes, so perhaps that has lodged something in the valve and is preventing it from closing as you say?? I running out of ideas... Will keep you posted. Thanks again for your post

Wouldn’t the pump turn off when it senses the boiler is full , ie independent of solenoid?

If you aren’t sure in the probe connection you could swap them around. I would guess one is a low level, one of a high level.

Or trace the wires to see where they are connected and compare to your friends machine.

These have a controller don’t they? Maybe that is playing up? Also a relay from memory.

As you have a friend with the same machine, you could swap parts to eliminate / confirm what’s gone wrong.

Don’t forget to unplug before tinkering.

Cheers

So it has a 3 way on the T, and that soienoid chooses if water goes to the boiler or the group?
So I was thinking if you choose group, but the solenoid is allowing water to pass to the boiler (leak, scale, wear, bad/wrong connection etc). Then despite the level probes telling the controller the boiler is full, it will keep filling as the machine doesn't realise it's leaking past the solenoid.

How to test....needs to go to a sparky.
Careful, the solenoid coils are 240v powered. Everything inside these boxes is bitey.
If I was a sparky looking at your machine, I'd undo solenoid output pipe to the boiler, then pull a shot with the blind filter fitted, or a pressure gauge portafilter. This will pressurise the group head delivery to full pressure and allow you to see if anything is coming out the boiler fill.

I would have disabled the boiler heater so the machine is cold, and the disconnected pipe would have a tail to a container.

But check your connections at that solenoid first, and the wiring, and maybe pull the solenoid apart for a clean. The top unscrews and remove plunger etc.

Hey esendee,
The BZ99 does have 2 solenoids, a 2-way for boiler fill and a 3-way for brewing.
From what you've described, it sounds like the boiler overfilling is happening when you try to run water from the group which indicates that water that should be going through the HX system is leaking into the boiler. If that's the case, you likely either have the boiler fill solenoid not closing properly, either from some grit in the valve, which could be cleaned out if you pull apart the valve, or the seal in the valve is worn, in which case you'd need to replace the valve. The other potential cause is a crack in the HX pipe, causing water to leak into the boiler when you brew.

My Musica is like that also. A 2way opens the brew path to fill the boiler

Originally Posted by Sir

Hey esendee,
The BZ99 does have 2 solenoids, a 2-way for boiler fill and a 3-way for brewing.
From what you've described, it sounds like the boiler overfilling is happening when you try to run water from the group which indicates that water that should be going through the HX system is leaking into the boiler. If that's the case, you likely either have the boiler fill solenoid not closing properly, either from some grit in the valve, which could be cleaned out if you pull apart the valve, or the seal in the valve is worn, in which case you'd need to replace the valve. The other potential cause is a crack in the HX pipe, causing water to leak into the boiler when you brew.

Hello Sir,
Thanks for the clarification on the solenoids. Still learning. If I run the group with no pressure, it seems to run just fine. But as soon as there is any pressure at the head, either back flushing or trying to pull a shot, that’s when the overfilling starts. After that, the steam wand only produces water - it seems that pressure at the grouphead somehow forces water back into the boiler? If I run the hot water for 20secs or so, it drains the boiler enough to produce steam again. So the overfilling is happening not just from running water through the group but when doing so while there is some resistance at the grouphead . Really appreciate everyone’s input. Will pull out and clean the solenoids for a start and see what results.

No worries. Only happening when the group in under pressure, with either coffee of blind filter would make sense with either the boiler fill solenoid not closing properly or a small crack in the HX. The water is going to take the path of least resistance, so if you just run water from the group with nothing in it, then it's going to mostly flow out of the group, but once you restrict that route, if there is an easier route for the water to go, it's going to find it, in this case into the boiler.
But what you're doing in cleaning out the boiler fill solenoid would be the best place to start so hopefully it will sort the issue out

try it with the boiler fill solenoid disconnected, this would rule out controller giving wrong signal.

then the above info makes sense, it would point to either leaking boiler fill solenoid letting water into boiler or leaking HX tube.

when the boiler is too full there will be no steam as it has been displaced by water.

cheers

Hi again everyone,

Well, I’m a happy man! Thanks everyone for for pointing me in the right direction. Opened up the 2 way on the boiler today. Sure enough, some gunk lodged in the valve. Closed it back up, and the demons are gone. Everything back to normal. Enjoying a delicious flat white as I type. First real problem with the BZ99 (picked it up about 3 years ago and have never done any work besides general cleaning and maintenance). Thanks again for all the great advice. Hopefully I’ll be able give back at some point.

Good work. Glad to hear everything is back on track.
Yo might want to look into the Water Filter Thread here and research.
If you haven't already.

I drink rum, and I collect the old paper $100 notes.

Good to hear it was a easy fix