anyone noticed that heater have internal thermostat that switches them off, while the

[KevinK]

this could be the one,

if you think about it, how can it (when not controlled by a external device) read accurate temperatures if it is surrounded by warmer water around the tube, or a warmer internal temp in the tube.

this would mean that it will go off each ... sec for a little while to get a reading, and if not at the desired temp, it kicks on again