I have had the same problem twice recently, and can safely say it depends on the set up, and the fish also.
I had two air rings in my tank and two fluval filters, and a air wall, and a 18month old newatt 200w heater.
It appears the heater stuck on as well and what drew my attention to the tank was my bumble bee catfish were
doing somersaults round the air rings and the albino pleco were congregating around the filters.
Infact 2 albino pleco's were about one inch above the water line and clearly looked like they
were trying to get out of the tank.
I have two thermometers in that tank- one of the electronic ones stuck to the glass which was not reading as the water was higher temp than its maximum, and the other is a hagen thermometer.
My Hagen thermometer showed a reading of 92-94 when I realised some thing was wrong.
I immediately turned the heater off and isolated that into a spare bucket of water.
I then did a 40% water change over a 1 hour period to try to bring the water down to a safe limit.
I was very lucky I only lost 2 guppies which were egg bearing at the time.
All my albino pleco's, a breeding pair of ancistrus pleco, and my prize show L71 peppermints
all seemed to pull through.
So I was over the moon not to lose any other than the ones I did.
Just hope it never happens again as twice in a month can be very bad for your heart
The tank appears to be stabilised now with a new heater, though even new ones can be faulty,
it took me two days to stabilise the new one as the setting adjuster is not as accurate as I liked.
Just done my water change on the same tank tonight and they all appear ok.
And as I mentioned earlier in another thread- it looks like some of my guppies are carrying again,
as well as my female bumble bee cat fish...
So I do hope you do not have any losses.
Please keep us updated.