I seem to have no control over my water temperature its at 28 was at 27 yesturday and the heater is set to 23 and it is only a 5month old heater. The tank has an apple snail and a plec plus 10 barbs in it.
If the house doesn't have central heating and you aren't in the middle of a summer heat wave, I would say you have a dodgy heater or the heater is way too big for the tank. But even if it is too big for the tank it should still hold a stabile temperature. Take it back to the shop and claim it under warranty.