Despite the UK heatwave settling down and my room becoming much cooler. My heater is set on 24c and even then my thermometer reads 31c with lights on and 29c without them? What's going on?
try putting the thermometer in the center of your tank for 30 minutes or so and then read it.
if you are using a digital thermometer it may be "out" by any number of degrees, perhaps the battery is run down?
also, the thermostat setting on most heaters is only approximate and cannot really be relied upon.
i would get a second thermometer as they are cheap enough online and can be delivered quickly.
Am having the same issues with my temp,all i do is leave the heater off until it drop to 25-26 then back on again,i use 2 thermometers 1 digital and 1you stick on the outside off the tank and they both read the exact same,it will all settle in time
As long as your fish aren't struggling, high temperatures are nothing to worry about. The main risk is lack of oxygen, as warm water holds less than cold. If you see your fish gasping or hanging around at the surface, you may need to add extra aeration or lower the water level (or raise the filter) to create more turbulence.
You could do a partial water change with colder water. You could also try unplugging the heater for some time to see if you maybe have a heater malfunction.