Bubbles from my heater

[Vincent100]

Hi r2r
Just cleaned out my sump ,took my heater out while I cleaned
After putting it back and switching it on loads of bubbles came out of the bit that you adjust the heat from
It's a jewel aquaheat 300w
Is this normal or is it now broke ,iv got it turned off at the min , iv a smaller heater as back up
Just think it's strange how the bubbles only came out once it was plugged in
Any info would be great thanks
The bubbles in the pic are from my skimmer lol

 

[Reeferdood]

If it is still working I'm sure it is fine. As for heaters though, I would try to keep that end out of the water entirely. There is a water line printed on the glass somewhere, right?