Argh Stupid Heater!

[tibby25731]

Got home tonight and realised the water in my 210 litre was much cooler than usual. Temp had dropped down to 74 degrees, I usually keep it at 80! The light on the heater was out, so changed the fuse in the plug and still nothing Ran out to Pets at Home - yes they do come in handy when it is 7pm and you have an emergency! - and bought a new heater, a Visitherm 300w. Same as the last, very old one actually!
So it's been in there nearly 2 hours now. Set it to 80 degrees. Temp is now 75 degrees, but the light on the heater keeps going on and off. I thought the light comes on when the temp drops below the set temp? So why is it not on all the time, till it gets to 80??? I am confused... Have set the heater to 86 in case it has been set wrong, and thinks 80 is actually 76 or something... still, it is on and off. Just realised I should pop a different thermometer in too, just in case.... but the water still feels cool to the touch so I don't think the thermometer is wrong.
Should I be worrying

 

[jourdy288]

Your fish should be OK, what do you have in there? You have it good, my heater went backwards and cooked my cory cat.

 

[fishyfreak]

Be patient, I think it's a safety feature so the heater doesn't get too hot. You don't want to raise it that fast anyways.

 

[OldMan47]

The heater is affected by the water right around it. When that water gets to the set temperature the heater goes off. A 300W is a large heater that will quickly heat the water right around it. If there is nothing to move water past the heater, it will cycle on and off based on the heat it is putting into the water. Do not raise the temperature higher than you want your tank because sooner or later the heater will have the whole tank at that temperature. Instead, make sure you have good water flow at the heater so it doesn't end up controlling a warm spot in the tank but gets to measure the real tank temperature.