86 degrees is not warm enough for many reptiles, so I would suspect the UTH is defective if it doesn't heat up more than that within a few hours. Personally, I don't like the UTHs that adhere to the bottom of a tank. I use Cobra heat mats or the equivalent sold by the Bean Farm (made by the same company) and use foil tape to attach them. An 11" x 11" one is $20 plus shipping at the Bean Farm, and they are great to deal with. Try Outback Reptile Co. for a thermostat. Their show prices are very good, but I'm not sure about on their website. Don't get a thermostat at Petco, you'll pay way more than you need to.
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Sohni
(aka Jeannie, but other people have similar names, too confusing, so I switched)
0.1 Baja de L.A. Rosy Boa (Bella)
0.1 Okeetee Corn Snake (Bess)
1.1 Rubber Boas (Esther & Isaiah)
1.0 Leopard Gecko (George)
0.0.1 Hermann's Tortoise (Moxie)
2.0 Adopted DSH Cats (Amos & Silas)
1.0 Rescued English Springer Spaniel (Jimmy)
and...
2.0 Kids (Riley & Noah) w/ 0.0.1 California King
Snake (Rex), 1.0 Mexican Rosy Boa (Lucas), 0.1
Leopard Gecko (Geico)
1.0 Husband (no pets, just us, lol)