Would be nice if they labeled each SSR so the user doesn't have to figure it out Perhaps they are in label order?

My money is on the sensor... or the PID. Check the sensor lead where it connects to the PID. If there is an extension, check connections there as well. You might try replugging them as sometimes a little crud can cause weird behaviour.

If you replace the sensor, make sure that all bends are large radius, with no sharp kinks or strain, particularly near connections.

At least you'll have a spare SSR.

Doubt this will really help, but I experienced the same exact issue with my Vetrano a few weeks into using it. After a week or two, the issue resolved itself, and the Vetrano's been steaming without issue for the past year or so. So my recommendation, procrastination seemed to work for me. That said, it makes me wonder if it's more mechanical rather than electrical. My disclaimer...while I know how to use the machine, I have very limited knowledge in how it works. Best of luck!

I have almost the exact same problem. Only difference is it never happens when I have my steam boiler at the stock 253 degrees (about 1.4 bars), but sometimes I'm making 4 drinks in a row so I crank up my temp to the 263 max (about 1.7 bars) to get things done quicker and that's when the OPV opens up into the drip tray. The machine seems to not know what the steam boiler temp is and I've seen the steam boiler jumping between 240ish and as high as 290 with the steam pressure needle just buried and all well after the machine is warmed up. My guess would be a faulty temp sensor and when the PID says 240 it may actually be at 263 but the machine heats up the steam boiler another 23 degrees which puts it up to 286 but the PID thinks it's at the right temp of 263.

I'm interested in seeing where you end up with Chris support. I'll bug them after you blaze the trail

I installed the replacement relay. Chris instructed me to change the relay whose wires went to the steam boiler. Unfortunately the switched wires from both relays dissappear into a rats nest of wires underneath the steam boiler, so it wasn't obvious which relay to change. I changed the one on the right size of the machine (or on the left as viewed from the rear) whose terminals were labelled K2. If anyone has a QM67 and can confirm I got it right, please let me know. Otherwise I'll check with Chris tomorrow.

Not surprisingly, changing the relay did not fix the problem. So assuming I changed the correct relay, I guess the next step will be to change the temperature sensor.

coffee boiler and steam boiler heating elements has different phase color wires from the relay, so you can check what wires color are connected to the steam boiler heating element.

Unfortunately that's not the case for my machine. For both relays, the input wires are black and white, and the output (switched wires) are brown. See photo. The 2nd relay in the background is a bit hard to see, but the brown output wires are on its top. Note that it's rotated 90° from the relay in the foreground. It did look to me like the K1 wires were going to the brew boiler, although I'm not 100% sure, which would mean the K2 wires go to the steam boiler.

black and white are the low voltage signal wires from the PID to the SSR ( solid state relay), anyway the K2 is usually for steam boiler ( 2nd channel of the PID) just be sure you respected the polarity +/- .

On a cold machine, remove one of the K2+ wires from one of the SSR. Power the machine. The boiler that remains cold is the one with the disconnected lead.

I've been away from my machine for a while, but last Friday I finally tried to install the replacement steam boiler temperature sensor I received from Chris Coffee. Unfortunately I was unable to remove the old sensor which was threaded into the boiler extremely tightly. When I attempted to unscrew the sensor with a crescent wrench, the entire boiler rotated, and I was worried I would damage its copper pipe fittings.

I called Chris's tech support by phone, and they suggested tapping the end of the wrench with a hammer. That failed to loosen the sensor.

At that point I had run out of time, and I gave up and put the machine back together. I did run the machine for about 1/2 hour with the cover off to ensure I hadn't loosened the sensor enough to cause a leak.

The good news is that I seem to have fixed the problem. Prior to attempting the sensor replacement, my machine would consistently overheat every time after steaming milk. I've not observed the problem since then.

It's possible that my problem was caused by a loose connection at the PID. I found that both boilers sensors connectors at the PID were very finicky. I had to unplug the coffee boiler sensor to get physical access to the steam boiler sensor's connector. When I plugged both sensors back in, I initially got A01 errors from the PID. After a bit of fiddling with the connectors, the error went away and the machine worked normally. It's also possible there was a loose connection where the cable enters the sensor probe, as I had moved the cable around while trying to unscrew the sensor.

If the overheating problem does reoccur, I will make another attempt to replace the temperature sensor. If anyone has any suggestions on how to restrain the boiler, or other ideas on how to remove the sensor without damaging the machine, please let me know.

When working on connections that could be cemented with scale, the fitting may be easier to remove when hot.

In any event, always stabilize the boiler with a strap wrench or a robust lever between robust boiler fittings.

Either use a flare nut wrench or slip a box end spanner down the cable to remove the sensor. 12pt box end allow 2x angle positions relative to flare nut wrenches, but risk more damage to an intractable soft brass fitting.

Intermittent connections usually re-appear.
The cable junction at the sensor is relatively fragile in some implementations.