Quick help with heater

[marco333]

When I bought my Topfin heater, it came with a rubber cap on the end. Is this cap suppost to stay on while in use, or was it only for protection while it was packaged. I've kept it on in the tank but it keeps poping off so im not sure if its suppost to be there. Here is a picture of it. The cap has fallen off and you can see it in the bottom left of the picture.
thanx

 

[alyssia]

I've never left the caps on my heaters

 

[mnm]

Probably a safety cap for those people who put them in an acrylic tank or sump so it doesn't melt the plastic. The heater itself is glass and can get quite warm, warm enough to damage acrylic.