I created a dashboard with a graph that shows the temperature of my heatpump system.
But after a hour or so my pi crashes.
Its a pi 4 with 4gb. I thought that such a simple graph should be a piece of cake for a pi to run.
The data is received every second by mqtt
What exactly do you mean by the pi crashing? Are you running the browser on the Pi? If so does it crash if the browser is not running?
If it is just the browser locking up then it may just be overloaded by the graph, though I would have thought a pi4 could have coped with it. A sample every second for an hour is 3600 points and since I imagine the graph is not 3000 pixels across that really is overkill. Try either slowing down the sample rate from the sensor or add a Delay node set to Rate Limit mode, one sample everly 10 seconds and drop intermediate messages and see what happens.
If it isn't that then stop node-red and start it in a terminal and post the startup log here. Leave the terminal open and see what it shows when the system crashes. .
Note: when someone asks what versions you are using and you say 'all latest versions' that doesn't help. Did you realize that NR v1.3.3 was released yesterday? By your statement I would have to assume you had it installed...but did you?
It also doesn't help someone in the future looking at your thread to see if your solution will help them. Not knowing the exact versions will make it hard for them to match your solution with their issue.