Hello all,

Had to do a descale on my Appartamento (grouphead suddenly felt cool to the touch). Something unexpected happened during the process: when backflushing the descale solution, the pump would stop after a few seconds. I went ahead regardless and once I had replaced the solution with fresh water, longer backflushes appeared to be possible again. Does anybody know what gives? Am I overlooking something?

Video here: https://streamable.com/e/d3k3ep

If you have any way of measuring the pressure in the brew circuit, you can determine the backpressure at which the pump stalls.
But really, it's going to be a weak pump, replacing the pump will fix it. When the components of the machine are all working well, the pump is easily able to continue moving water against well over 10 bars backpressure. The machine has an OPV that is forced open at about 10 bars, so the pump should never stop running.
If the OPV gets stuck shut, then the pump will continue to move water into the circuit until the pressure is high enough to pass the expansion valve OR stall the pump.
You can purchase little gauges that screw onto the existing threads of your portafilter (in place of the single or double spout). Or you can thread the portafilter to allow it to accept a gauge, if you really want to set your Pump OPV and expansion valves accurately.
https://ecscoffee.com/products/joefrex- ... 1332292666

TLDR: Replace the weak pump.

Thanks. The weird part is that it worked fine afterwards with fresh water... Anyway is it possible to swap out a vibe pump for a rotary one?

There isn't enough room in your machine for a rotary pump; compared to a vibe pump, they're huge. Also, the Apartemento is intentionally made on the smallish side.
As for the pump stalling (definitely from the sound on your video) then not stalling, it could be that your OPV was gummed up and then was freed after descaling. Too bad you didn't watch the return line for lack of water flow, which is a sure sign that this is happening for all but a nearly dead pump.
Hey, if it still works and produces adequate pressure, you're still good to go. But, vibe pumps are a replacement item and not expensive. I'd get a spare one for the eventual need to change the pump, if you plan to keep the machine.

Thanks. Yeah, guess I'll do that. The scale problem doesn't seem to be gone though, the brewhead still feels cooler than it's supposed to be. I suppose there's no other way than to disassemble the pipes and try and find the clog?

PS: while on the subject of pumps, is there a particular model you recommend?

I presume your machine, like most, has an ULKA pup. You should go with a pump that's the same as or similar to what you have. Here's an ULKA data sheet https://cdn.shopify.com/s/files/1/0632/ ... 1652137056 Frankly, there's little difference between these. Some have brass piston sleeves, some have plastic. There are variances in duty cycle (1/1, 1.5/1, 2/1). There's also some minor difference in power consumption (47 vs 54 Watts). They are all 15-bar pumps for espresso machines. You can get them from most espresso machine purveyors that sell parts, and also on Amazon. It may pay to shop around, as Amazon isn't necessarily the least expensive seller; as I recall, I got my last one at a reasonable price from IDC (Canada).