Hot end always ON!

[Morriz]

Anyone know what is the problem with my HE280 hot end:

When I power on my Rostock Max V3, hot end starts immediately with red light ON and warming the heater cartridge.
Termistore measure right temp, but I cant stop warming the hot end.

The problem started during the start on a print, when bed was right temp and hot end was warming to reach the right temp.

I thing the heater certridge is good beacause it warms hot end.
I think the thermal safety fuse is good because otherwise heater cartridge not warm.
I think the 100k thermistor is good because otherwise display dosn't increase hot end temp.

So what is it??

Marcello

[geneb]

This can happen if the Kapton tape on the thermal fuse isn't fully covering the fuse body where it mounts in the cold section of the hot end. If any bare portion of the fuse body comes into contact with the hot end, it will result in the effect you describe.

g.

[Morriz]

Thank you!
That was really this problem.

I moved just 2 mm on the right the thermal fuse and hot end and red led went OFF.

Stange but true!

Marcello

[geneb]

\o/

[Jimustanguitar]

This can happen if the Kapton tape on the thermal fuse isn't fully covering the fuse body where it mounts in the cold section of the hot end. If any bare portion of the fuse body comes into contact with the hot end, it will result in the effect you describe.

That kind of a short doesn't bypass the fuse, I hope...

[geneb]

The fuse is thermal Jim. If it gets too hot, it will do its job and die.

g.

[Jimustanguitar]

I wondered if the heater would pull ground through the metal can regardless of whether the fuse was open or not... That's what I was getting at.

[geneb]

I don't think so. It's my understanding that the hot side is the common plane, not ground. (ground is switched...)

g.