I'm having a pump pressure issue on a profitec pro 500 PID machine.

I replaced the solid state relay and descaled the machine yesterday

Today the machine started to act up
- the first shot was OK
- on the second shot the pump stopped about 15 seconds into the extraction
- on the third shot, about 10-15 seconds in, the pressure dropped from the usual spot around 9 bars to 8, the it would go back to 9, and cycle like that until the completion of the shot. I could hear the pump sound go up and down accordingly

The machine is about 4 years old. Aside from the usual SSR replacement it has worked reliably.

Does he SSR also control the pump, or just the temperature.

Any ideas how to troubleshoot from here?

You can hear the pump change a little as the SSR turns on and off in almost all vibe-pump espresso machines. It's because the power draw of the element when the SSR is on causes a slight drop in the power to the pump.

If it is extreme, you need to start measuring the voltage at your outlet, your power switch and other connections to find out where the voltage drop is occurring, but so long as it's just a slight change in the hum of the pump and a 0.1 bar shift on the needle of the pump manometer, it's normal. (European machines show it less, they run at half the current, so their engineers don't care to wire the machines they export to us with decent 14 gauge throughout the load circuits).

It's definitely more than 0.1. More like 1-1.5 bar. And one time it just stopped pumping water all together.

The power outlets are the same as before I replaced the ssr. So I don't think the problem comes from there

I might put the old Ssr back in and see what happens.

It could be that the pump is getting weak. If you run the pump with the valves closed, does the pump just stall?

The pump runs fine when there is no coffee in the portafilter. The problem is intermittent. I took everything apart and put it back together, and it worked fine a couple of times yesterday. But now it's back.

I probably should have made one change at a time
- replace SSR and check everything is working fine
- descale and check.

But I figured I would do all the maintenance while the machine was taken apart.

Wondering if it's related to the descaling and some is obstructing the pump.

Here is a video of the problem

Yes.
Your pump is dying. It's stalling at less than 10 Bar. Your new pump will fix your issue.

I noticed that during the shot when you lose the brew pressure the pump goes completely quiet. That to me is clear sign of power interruption to the pump, and I can think of a few causes, 1, the pump's coil has failed, 2, the over temperature switch (that attached to the outside of the pump coil) has failed, 3, the Gicar controller has failed, 4, a combination of the above.

If you know how to and are comfortable with working around the mains power, it may worth a couple simple tests to rule out some obvious before ordering parts, such as, 1. monitor the voltage across the pump terminals during a shot and confirm/dismiss the power loss when there is a pressure loss, 2. hard wire the pump, with the temperature switch in circuit, to the 120V mains supply, brew into the backflush disc, and see if the power interruption replicates, then, 3, hard wire the pump, this time with the temperature switch out of circuit, to the mains supply, brew into the backflush disc, and see if the power interruption replicates.

By the way, the SSR in pro500PID controls the boiler heater only.

EDIT: I watched that video again with sound volume all the way to the max, and realized the pump did not go completely quiet and did put out some subdued humming noise. I think that should rule out possibility of outright power interruption, and make the pump itself the primary suspect. There could be small chances that debris could clog the pump outlet from inside the pump and that would stop it from vibration.

I've had the same issue, almost always after descaling or running cleaning flush rubric. Sometimes it happens after it's been powered up and idling for a while, so I'm guessing that there is a temperature sensor OR a pressure sensor that is sensitive, for some reason, to heat?