Heater not holding temp

[Dinodanger]

I’ve got a new heater And I left the window open all night, where I live is quite cold so the house would be around 10-13c, my temp controller Alarm went off with tank temp being 24.5 from what it should be 25.6 shouldn’t a brand new 300w TMC heater keep that temperature or do they only heat from room temperature? The tanks a 250litre

 

[Jonesyg]

I would imagine the tolerence between the heater coming on and off is +- 1 deg at least, in my experience ive never found a heater which self regulates that accurately. I now use an external controller which is much better.

 

[Dinodanger]

I would imagine the tolerence between the heater coming on and off is +- 1 deg at least, in my experience ive never found a heater which self regulates that accurately. I now use an external controller which is much better.

Yeah I’m using a external controller

 

[Jonesyg]

Do you have the heater turned up to full on the heater itself? Thats normally what you do when running an external controller otherwise your still using the heaters internal controller in parallel. I set mine to max then backed it off a bit for security incase the controller gets stuck in the "on" position for some reason.

 

[Dinodanger]

Do you have the heater turned up to full on the heater itself? Thats normally what you do when running an external controller otherwise your still using the heaters internal controller in parallel. I set mine to max then backed it off a bit for security incase the controller gets stuck in the "on" position for some reason.

Yeah I did that