Always check your heaters!

[Graham]

So today I decided to do a thorough look at each and every one of my heaters just to make sure they were all working properly.They are all 200 watt eheim jagars, and turns out the one on the tank with my most expensive fish was faulty! It heated the water to 76.8 F and then would short out. Very weird. Luckily I had another spare heater on hand. So just goes to show, even if you have quality equipment, things can go wrong so it doesn't hurt to check. I'm going to try and get a refund through the 3 year warranty. Just thought i'd let everyone know!

[Al]

Graham, I keep a digital thermostat on top of each tank, that has a high/low reading capability as well as current reading and at a glance, while walking around my tanks or the basement, I can have a quick glance at anything going askew. The readouts are large enough that I can read them from 3-4 feet away. But agreed, nevertheless, we always have to be vigilant as components do breakdown and fail. On all of my large tanks, where I have 2 or more heaters working, I always have the heaters running through a separate controller as a double fail-safe - the heaters plug into the controller and it is the controller that regulates the heat control function and turns the power on/off to the heaters.

[wolfiewill]

I keep a digital thermostat on top of each tank, that has a high/low reading capability as well as current reading and at a glance, while walking around my tanks or the basement, I can have a quick glance at anything going askew. The readouts are large enough that I can read them from 3-4 feet away.

Al, what model of thermostat are you using? I'm having too much trouble seeing my in-tank glass ones to do a quick check.

[Al]

I have used several over the years - right now I am using thermometers from the control company, models 4121 and 4048 which I purchased from Canada Wide Scientific on Walkley Road - I set up an account there. I noticed they recently raised prices because of US origin and they are now ~ $60, used to be around $45. These thermometers are certified and I found them to last extremely well versus most of the cheaper digitals - they are also more accurate when compared to a standard thermometer reading as they are certified because they are being used in lab environments.
I even use a digital when I am doing water changes - as I run the python filler in my sink I have a digital with the probe wire in a yogurt container below the python, testing for water temp and when I reach my ideal, I lock my python in refill mode - the digital sits up on a shelf and it's dead simple to see rather than looking at some dinky small glass thermometer - especially with my old eyes.
Having said that, they key is not so much the accuracy but consistency. If the cheaper digital reads off a couple of degrees, so say it reads 79 when your glass thermometer reads 81 - as long as it keeps 79 you know you're good and many of the cheaper ones seem to be fairly consistent but they fail over time. I have run tests by putting several of the cheap style digitals in the same tank, the cheaper digitals like marina and coral-life and there would be differences of 2-3-4 degrees (:<( - but again, you want consistency. I went through a lot of the cheaper digitals and just threw them away in the end.
These ones from Control Company have been rock solid and were a good investment in my books, although I appreciate not everyone wants to spend that kind of money on thermometers - but for me, it's no different than any other aquarium related investments - quality lasts. At the end of the day, a 7.99 digital from company x probably cost $1 to make and through successive markups it sells for 7.99 - it is what it is but you could get lucky.
Pets and ponds have a wide variety of digitals from 7.99 up to $25 for Lifegard models which I have would rate the best of the "cheaper digitals" I have tried with a nice sized readout and now I see they carry Pinpoint thermometers from American Marine at $39, however write-ups at Marine Depot aren't glowing.
Good luck.