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

[KrazyKuch]

I have a theory. I have never looked at the internals to a heater before. But it would make sense to me to pulse the heat on and off. For the thermistat to work properly you would want the heating element turned off so that you can get a better water temperature. Remember that it will be hotter inside the heater then out.

this is just a theory and not fact...now i feel the need to test this theory with my heaters!

[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

[mike31154]

Are all the heaters the same size/wattage? You mention they are different brands. Most are built pretty much the same with a simple bimetallic strip that switches them on/off. Dissimilar metals fused together bend at a different rate in relation to temperature. A set of contacts at the end make or break in response to the bending, completing or opening the circuit to the heating element.

Many things come in to play that influence the behaviour of the the bimetallic switch. Heater location (in relation to flow), size (both physical & wattage), variations/quality in manufacturing, water level in relation to the bimetallic strip, age of the heater, etc. Over time, the contacts become pitted & fail due to arcing every time they open/close. Pitting will increase contact resistance & alter the cycling rate of the heater, worst case they fuse together & the heater stays on as described by many folks who've had them fail that way.

Not sure having all three connected to a single channel on your controller is a good idea either. You've taken the redundancy of having 3 heaters & connected them to a single point of potential failure. Also make sure that the single channel you have them on is rated to handle the wattage of the 3 heaters. I assume it can, since it appears you've been running that way for a while, but never hurts to double check, since as mentioned, as contacts wear resistance increases and with it the actual power draw of each heater.