timer problems

having problems with tiers lataley not working like whats every 1 using, ive got 4 X 600 hps in 4 seperate plus could put them all together with an extension but a still need a timer that is reliable been thru 3 timesrs in 2 weeks and their not consistent, every time a go to my grow room the lights shud be off but their still on, never had this problems bepfre but its doin me head in now cos a cant get to the place where im growing every day, any help much appriciated