Can't switch to right nozzle

Bambu Lab H2 Series Bambu Lab H2D
1

When it tries to switch from left nozzle to right, it gets stuck on the way and doesn’t always recover. Looks like this when it succeeds:

Video Project 5

Anyone know what would cause that?

I’ve had a ticket open over 3 weeks, taken apart and examined the blocker, the arm that carries the blocker, the hotend heaters, the lifting slider and rail. When the left heater assembly is off it’s fine, when it’s on this happens, but I can’t see any part of anything being blocked or getting stuck.

Nothing looks damaged at all, there’s no filament or anything stuck anywhere, it’s all lubed and adjusted. I can’t feel anything unusual when I move it by hand in either direction.

Bambu wants to send a new lifting rail and heating assembly. I don’t have any other suggestions but I can’t see how either would help, there’s nothing wrong with them. I asked if they would send a lifting motor as well, jury’s still out.

I had just over 1000 hours on the printer, running it every day and everything’s fine, then I had a print where the prime tower got knocked over and now this. I expected to find the flow blocker or its supporting rod bent or hitting something but that’s not it, I can see every part of those and they’re completely unobstructed.

Ideas?

Thanks.

2

It could be an end switch or sensor not triggering properly.

Since you are mentioning heating is causing this to happen, it might be a poor connection or a hairline crack in a flex PCB that disconnects when it warms up.

3

Thank you for guessing. The heating assembly is not operating, just its physical presence is enough to cause the sticking.

4

Then there is something blocking. Either a screw that is too long, or something else. Should be easy to trace, by removing screw by screw and test. Might also be something on the heating assembly itself.

5

Left ceramic seems cracked near the top bolt. All the red filament residue is disgusting, who knows what filtered behind the cradles…

6

There isn’t really red crud all over that. I was wearing a headlight and and mistakenly had it set to red when I took the video. Never thought about it till you said.

The left heating assembly is not cracked, that’s a shadow of the bolt recess.

7

There wasn’t anything mechanical. Replacing the heater assembly seems to have fixed it, though I can’t test because now something else has gone wrong. Personally I think it was a sensor problem.