i agree i have also heard of mechanical timers failing but only after a period of use, the digital timers i had went a bit crazy, instead of only having 24 hours to a day, it just kept going past 23:59, it carried on all the way up till 44:59, so i have not used either off them since, they worked good for the first week or so, i chose the digital ones as they have some battery in them so even if their is a power cut they still keep time, so then when the power comes back on they can return to how they was, maybe i got some cheap ones that wasnt much good, people use both types of timer and have no problems, so maybe i just got a bad batch, but they did work again after i reset them and i had no problems since, but now im not running a hydro set up with a pump i have not needed to use the digital ones, so their sitting in the cupboard doing nothing at the moment,