Breville Dual Boiler short circuit: Brew pressure doesn't fall after shot

Equipment doesn't work? Troubleshooting? If you're handy, members can help.

#1: Post by mikegray »

Ugh - I think I've messed up bad!

I got a used and abused BDB 920XL cheap. It worked, but pressure readings were all over the place, so I ordered a replacement pump and brass OPV, followed instructions (in a youtube video linked quite often here) - and everything worked PERFECTLY.

The sad part: When I ordered the replacement pump and OPV, I ALSO ordered a new solenoid valve, just in case. I'm pretty sure the old one was fine - but I got so cocky about the work I'd done on the pump and OPV that I decided to swap in the new solenoid as well, "just to make sure."

While I was unscrewing the old solenoid I forgot to unplug the machine. I made a funny movement, saw a spark, got a shock - and the kitchen circuit breaker popped.

- I went ahead and installed the new solenoid.

- Now, when I pull a shot the pressure is still perfect.

However, when I stop the shot, the lights go off and the pump stops - BUT: the pressure in the system doesn't release. That is, it just sinks very, VERY slowly. If I have the backflush rubber in, the pressure falls to about 7 then sticks. When I pull out the portafilter the water kind of gushes/sprays. If I have coffee in the portafilter, the coffee just keeps running slowly for a minute or so.

I can actually make a good coffee this way - just have to pull the cup out of the way when I'm done - but it's a mess and utterly NOT wife friendly! Is there any chance I can fix this or have I just ruined my machine?


#2: Post by luvmy40 »

Your three way solenoid is probably not switching to vent the group pressure. Trace the wires from the solenoid back and look for any break in a wire or if there is a burned spot or fuse on the board they go to(come from).

This is just a logical progression. I have never traced this circuit before on the BDB, there may be something simple or obvious with this that I am unaware of.

mikegray (original poster)

#3: Post by mikegray (original poster) replying to luvmy40 »

Thanks. Yeah - I think that's what has happened. In fact, I discovered that if I leave the top off, manually pull a shot, then yank one of the two power wires, the solenoid will switch and release pressure. (Probably not something I should doing much, but it makes it VERY clear where the problem is - and also that the problem has nothing to do with the solenoid valve itself.)

The solenoid has two live wires - the white wire goes back to the pump, the yellow one goes to the mainboard. Sadly, upon opening up the mainboard, I couldn't find any sign of damage anywhere.

A VERY quick and dirty solution would be to wire a switch into one of the lines - that would have me making coffee again, but it obviously doesn't solve whatever is really wrong with the machine. Also: I had the machine open and plugged in this morning and just set my elbow on the outside edge - and got another shock, full 220v. So, clearly something is not good in there, and I'm getting a bad feeling about this.

Sadly, I'm afraid the machine may be on its way to the landfill. :(
- While Breville (at least in the US?) has a generous program for units out of guarantee, my unit was marketed by a German company called Gastroback. They don't sell the 920xl anymore, and I haven't even got any replies to my queries.
- I could order a replacement mainboard from Australia. But without knowing whether the mainboard is actually the source of the problem, I'd be embarking on a VERY complicated repair job that might not even be the problem.


Team HB

#4: Post by JRising »

mikegray wrote: I had the machine open and plugged in this morning and just set my elbow on the outside edge - and got another shock, full 220v. So, clearly something is not good in there, and I'm getting a bad feeling about this.
Okay. So it's shorted to ground, it's possibly not a problem with the powerboard. Once powered up, the three-way switches to brew position (closed off drain), When done brewing it should switch back to closed off boiler, but the neutral is shorted to ground somewhere providing a path for the current, thus the valve stays open. It is possible that it is the coil itself, step 1 put your old coil back in, on the new three-way valve.
If still no good, follow your neutral component to component, If you're lucky, the short is bad enough to detect with a hand-held ohmeter. If so, you can unplug-replug wires and components to trace it.

mikegray (original poster)

#5: Post by mikegray (original poster) replying to JRising »


Thanks for this help, let's at least take a shot at this before I throw in the towel. I've tried to document my observations as best I possibly can. (Note: While I do actually own an ohmmeter, I've sadly never learned what to do with it, so I'll ALSO need someone to tell what to do with the things - see below ... )

Shot one is of the solenoid valve. (I have tried both the old and the new valve - there is NO DIFFERENCE - both have the same problem.) It has a ground cable and two other wires: white and yellow. I don't know which is neutral.

Shot two, I follow the yellow wire to the mainboard, where it plugs into a spot with marked "solenoid". I notice that there is ANOTHER yellow wire fairly close to it it, marked "S-PUMP." Maybe I should follow it?

Shot three, I follow the white wire to a splitter.

Shot four, I follow one branch of the white wire to someplace right in the middle of the mainboard.

Shot five, I follow the other white branch to the main pump (the new ULKA EX5). Another branch travels from here to the steampump.

Shot six. Very embarrassing, but this is my ohmmeter. It has dials and little stabby things. Presumably, I turn the dials, then poke things with the stabby parts - but I honestly don't have a clue how or what!

Team HB

#6: Post by JRising »

Sorry. I shouldn't give electrical advice here at 7:20 AM, I forget the "don't electrocute yourself" step.

Okay. The white goes to that split connection, it's common to all components, based on this, in order for my "Short to ground providing circuit to keep solenoid live theory" to be accurate, white would be phase and yellow is switched to neutral at the powerboard.
For fun, with the ohmeter where it's set in the pic so it's measuring in the thousand ohms range, stab a stabby thing into that white that you're holding in the pic with the 2 drawn in, and the other stabby thing stab a good ground, body metal or any of the connectors on the green/yellow-stripe ground wires. If your needle moves you're proving that something shorts to ground somewhere. Then try again with one stabby on yellow and the other on good ground...

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#7: Post by Psyd »

Just a quick lesson on the multimeter:
You're not set correctly, you're testing at 'times a thousand Ohms' with that setting. Try the 'times ten'. The meter shows how much of the battery's onboard electricity passes through the leads, and the green scale at the top is graduated in Ohms. The more resistance (Ohms) the less electricity passes.
Test this with the leads away from one another; it should be maxed at the left end of the scale, or 'no electricity passing'. Touching the two leads together should show all the way to the right, or 'all the electricity passing'.
Espresso Sniper
One Shot, One Kill

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