brrrrrrrrrrr!!!

I don't know how most people check their heaters, but I usually give all my tanks a glance each night to see if the heaters lights are on.

Yesterday, not thinking I had a problem, I started my water changes on my fry tanks, I realised one wasn't as warm as the others, I put in a thermometer just to confirm, sure enough was considerably cooler than the others, I finished my water changes, put heaters back on, lights all on................. not happy about this one tank, I ummmed and ahhhed for a while, but decided as I had a spare heater to swap it, I realised the babies weren't moving about as much as the other tanks, so thought it best.

This morning, temperature back up to where I was happy............... hubby put the old heater in a bottle of cold water, light came on but no heat!! Its now in the bin!! Had I not been doing so regular water changes I might have missed this fault, thinking perhaps I should have two heaters in my tanks!! Having said that in the 30 years of keeping fish this is the first time I've had the problem............... also it was a cheap heater (as it was only a fry tank) off ebay, I'm now thinking cutting corners doesn't pay!! I have one more of these heaters and I shall be keeping a close eye on it!!

Glad you caught it in time.
Having two lower wattage heaters is a good idea, especially in larger tanks, where you are likely to have a greater value of stock.
The most common problem with heaters is wear of the bi-metal strip in the thermostat, due to sparking each time it opens or closes. If you have two heaters set to slightly different temperatures, one will usually be on. Should it happen to stick on, it won't be powerful enough to take the temperature too high. Should it stick off, the second will cut in when the temperature drops slightly. In both, the bi-metal strip will suffer less wear since they will spend most of their time either off, in the case of the one set to a lower temperature, or on, in the case of the other. So not only do they protect against the effects of one of them failing, the likelihood of either failing is reduced.