My machine turns on and warms up nominally, all lights turning on, but the moment I try to pour a shot of espresso, it trips the GFCI breaker. Every time I press the 1 or 2 cup button, the breaker trips.

So I opened the machine up and found no source for heavy leak, but did find a burnt wire over the heater/boiler, and the ground screw at the base of the machine rusted.

Any suggestions?

Here's an image of the burnt cable over the boiler ...



Here's an image of the rusty screw ...







-Jonathan

That cooked spade connector is on the hi limit safety switch of the same type I've had (evidently) short to ground before, but that was in the presence of water escaping an anti-vac valve that your machine doesn't have (as there is no boiler)

The good news is that those are cheap and easy to replace (doing so solved a similar GFCI-tripping issue I had), the bad news is that there really isn't anything that should be exposing that to moisture...you might wanna do some at-temp cover-off troubleshooting to see if the steam/water selector or something is leaking.

If you have a multimeter - check continuity between either terminal on that hi limit switch (it should be closed unless overheated, so either one works) and A) the side of the thermoblock and B) any of the grounding terminals. Should read as an open circuit - if you see low resistance there, that'd reasonably confirm the source of your short and outlet-tripping. It's inline with the valves and pump so activating brew or steam would introduce current to the ground pin that your GFCI isn't happy about.

EDIT: if you don't have a meter, you may be able to empirically test by TEMPORARILY separating the hi-limit switch from the thermoblock (leave the wires connected but unscrew its hold downs, unstick the thermal paste and perhaps wrap in electrical tape or other insulator to isolate it from the thermoblock without your hands in there because it sees full AC mains voltage)... if you can run the pump /brew cycle without tripping the outlet, that's probably the culprit. Just make sure the machine is physically unplugged when handling any of this, and that a functioning hi-limit is back in place before you operate the machine for anything other than diagnostic purposes...DO NOT leave it isolated.

...but also if you don't have a meter, get a meter

If I recall correctly, that machine runs the pump a few seconds on startup to supply water to the thermoblock....is it making it through that without tripping your outlet?

Extremely grateful for your reply DefaultIT,

I will get myself a meter and try measuring as you've outlined.

As to your final question, the machine is indeed running the pump for a few seconds on initial startup/warmup without any issues. The trip occurs only when I attempt to brew a shot.

I agree about not liking the looks of that one wire, its burnt insulation and all... But it doesn't look shorted to ground, it might be a symptom of the heating element in that boiler shorting to ground and drawing far too much current on that wire that we can see.

Keep us posted with your multimeter readings and let's see if we can advise further, but I believe you'll find a short from either or both element connections to ground on that one boiler.

But... Because I can, I'm going to second guess myself...
Your machine can complete boiler-fill without tripping... Then heats the boiler without tripping... It isn't until it tries a function where it:
Starts the pump and runs for a split second, then opens the Brew Solenoid Valve... And trips at exactly that stage...
Also test for shorts on the coil of the brew-valve. I hope you get where I'm going, here, just kinda thinking out loud, but in text.

Agree that if it's making it through startup, both the pump (which runs for a few seconds) and the heating element (which preheats) are energized without triggering a fault, which I think leaves the solenoid valves.

Again JUST FOR TESTING PURPOSES you can probably pull the green ground spade connector from each of the valves respectively (they're those 2 black rectangular boxes with 3 connectors each) and see if that stops your GFI tripping. Those coils are also pretty easy to replace

..tip: Breville uses locking spades, so they will be pretty stubborn. If you want to make it easier, have a look at the one that's cooked and you'll see a little tab right where the wire terminates (between that second crimp and the spade itself) that can be depressed to release a little lug and engages the hole one the male (valve side) prongs. [Actually looking at your pic again I guess the ground spades aren't under heat shrink, so just look for that little tab if they're not coming off easily)

Alright,
Got the meter and started measuring around. As far as I can tell, I found no short. Found perfect continuity between both terminals on that hi-limit switch. Found no short when testing one of the terminals against the wall of the thermablock. See image below (I know i went ahead and cut out the burnt cable, will have to replace that connection somehow) ....




To check for shorts on the solenoid valve, I checked between the positive terminal of the solenoid and the green bottom terminal, and there was no continuity. This is the right way to check for shorts, right? or am I missing something? See image below ...











....... Is there anything else I should measure?





-Jonathan

... also, on the two solenoid valves, I'm getting 530 and 440 ohms respectively on each.




-Jonathan