Longevity of plant propogation pad (ie, heating pad)?
 

Bought a "heating pad" plant propogation mat two seasons ago, it has
worked like a champ and really makes a huge difference for starting
seeds for me. I can get seeds germinating in three days, depending on
the variety.

Here;s the question: Is there a governor on these things so they don't
run for days and days? I check mine every day for sprouted veg, and
the last couple days I've checked the pad, it has been stone cold. I
could swear that last year it stayed warm overnight, as flats were
warm in the AM.

I wonder what the lifetime of these things might be.. I started
thinking about them when they were 14.95, bought mine at 19.95, now
they are up to 27.95, and I wonder - are these things real pieces of
junk?

Do the $70.00 versions last longer? I see people asking about medical
heat pads 'cause they are cheaper, and I know that's a bad combo -
water (seed flats) and electrical just don't play well together. I'm
willing to fork it over (I think) if the thing will last more than 3
seasons..

Any suggestions? The pad I have was not purchased from these folks,
but it looks like this:
http://homeharvest.com/propagationaids.htm

Search for: Single-Tray, 17 watt version measures 9 inches by 19.5
inches and holds one standard propagation tray

That's the kind of mat I have questions about. Are the heavy duty
mats better/last longer?
Any safe alternatives?

TIA