In the last year or so I'm using RO water with added minerals (either TWW or RPavlis formula), but I have to admit I wasn't so particular about water in the past. My machine works perfectly, but I wouldn't be surprised if there's some scale inside that's left over from the past. Should I descale it before attempting to install a grouphead thermometer and a flow-control device?

Thanks!

I'd pull the mushroom and inspect it for signs of excessive scale. If you don't find much, I'd not descale. Unless your water recipe is unusually high in hardness minerals, which is unlikely, chances are you have no "scale". Some soft deposits perhaps, but no hard scale. RO water is a natural and very gentle descaler in its own right. Indeed, some say that it will actually erode not just the scale, but also some metals.

As for your plan to add an FCD and a thermometer, are you sure you want to do this? I believe your EVO is an HX machine. If so, installing a thermometer such as the one from EricS is an excellent idea. However, doing so precludes installing the pressure gauge that comes with the FCD kit. On my HX, I considered the thermometer to be nearly essential. On my DB with FC, I consider my group pressure gauge to be essential.

Most likely if your machine has any scale, it's in the steam boiler. The HX circuit, which is separate, will only scale with hard water since you are constantly moving water through it. If the water you're using now is on the softer side, it can dissolve some light scale.

Thanks for the replies!

My machine uses a single-boiler, it's not an HX. It's on for about 5 hours a day but I almost never steam with it. If there's scale left from the days when I used hard water, would it make it difficult to pull the mushroom? And if it is difficult, is that a sign that descaling is needed?

I already bought the flow control device and the thermometer, but I'm not sure yet whether I'll keep the pressure gauge or the thermometer permanently. Since the machine is a single-boiler with PID I think I'll install the thermometer first, as it's less likely to be needed long term. I'll then experiment with it for a while, get better understanding of how the PID and flushing affect/reflect brew temperature, and then switch over to the FCD and pressure gauge. Does this plan make sense?

Since the machine is a single-boiler with PID I think I'll install the thermometer first, as it's less likely to be needed long term. I'll then experiment with it for a while, get better understanding of how the PID and flushing affect/reflect brew temperature, and then switch over to the FCD and pressure gauge. Does this plan make sense?

Sorry, I didn't realize your machine is an SBDU. My experience with these is decades old on a Silvia, so my advice may not count for much. Anyway, I think your plan is good. Use the thermometer to get a handle on brew temps, make adjustments as needed, then switch over to the FC pressure gauge. You could leave the thermometer on when you install the FC kit, for experimental purposes. But, to actually get the best out of the FC you need the pressure gauge.

+1 To all of Nunas' advice.