[Rooster]

Does it have a lamp, to say when the heater is on/off?
If so... Just turn it up until the heater comes on, leave it a hour and test temp again with thermometer - never trust the scale on a heater/thermostat!
If that works, keep turning it up a little at a time until you reach the temp you want.

If it has no lamp, you should be able to hear a "click" as the heater turns on/off...

Sent from my ZX81

 

[Rooster]

are you in a cold climate? if so... And you are using an external filter, the lag the filter with a blanket or similar.
if its an internal filter... I've no idea what's causing the problem, unless you electrics are faulty :-(
I'd buy another heater... It's wise to have a spare anyway.

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