I did the same thing as seangee. I had two heater failures in which they got stuck full on. I also know that heaters are the least reliable piece of equipment we put into tanks. Controllers are a decent solution but they are not foolproof, They too can fail. However, I had abut a dozen controllers working on tanks. When I downsized I sold 5. Since then I had my very first one fail.
Failure in this instance meant it stopped turning the heaters on and off it just let them stay on. But I bought most of my controllers quite a few years ago.
I also had no choice as to using them or not in most of my tanks as the fish I kept and bred were from places where the water is warm, it can even creep into the low 90sF. I kept most of the tanks at between 28C and 30C. My controllers were in C even though I live my life in F.
I had two heaters wipe out all of the fish in one tank and all but the plecos in the other.
Equipment failure is something that we all have to be prepared to handle. Filters, pumps, lights, chillers etc. etc. all can fail. What really matters most is how quickly we learn about a failure and deal with it.
I have used a variety of heater brands. In 2001 I felt Ebo Jager was the best brand to buy. I had one run for 19 years.. But things change and so did the quality of Ebos since they were acquired. Incidentally, the two failures I had were different name brands. The result of it all was for many tanks I selected my heaters by price. The less expensive the more I like them. However, there is a limit. I bought about a dozen really cheap heaters online from a reputable seller. They worked poorly. I use almost all heaters in a horizontal set-up close to the bottom of the tank.
The heater I got would not go on and off in the position. They worked OK when vertical and even angled a bit. But beyond the bit they quit. Cheaper heaters tend to be longer than the pricier ones. I use long shallow tanks and often divide them using a Poret sheet foam. I want a heater on each side of the divider. These heaters would only fit horizontally and vertically were too long. I have a box of them I would sell for $25
The most reliable heaters I have used and I still have 3 of them, are the Hydor Inlines. I had 3 running at one time. I use them with canister filters. I have had one fail, the very first one I got in about 2003. It failed in the past year. Fortunately, I can afford to put some extra equipment on the shelf. I grabbed a couple of extra Hydor Inlines when they were on sale some years ago. I try to stock spare parts as I also try to standardize my Equipment. It is what I love about Aquaclear hang-ons. A lot of the parts are used on more than just one model. At my peak I has 28 of them in all sizes running. I still have 12 in use.
I bought a lot of the AquaTop heaters from kensfish a number of years back when they were fitst sold there. They were very cheap. I sill have many of them today and they were a decent deal. They are as reliable, or moreso, as the pricier brands.
For those who might be interested in an inline heater, Hydor makes a 200w and a 300w. The 200w has 2 models which have different diameter hoses.
https://hydor.com/products/eth I paid a lot less than they cost now. I should note that in a bigger tank I will use both a Hydor and an in tank traditional heater.
(edited to fix typos)
PUBLIC SERVICE ANNOUNCEMENT 
