the duracraft thermostat in our rental does not seem to be working properly. it is set to always be at 74 degrees F. yet it has recently failed to do so and i've had to bump up the temp to 76 and hit "hold temp" to get the heater to kick on. to be safe, i put in new batteries even tho i put new ones in 8 weeks ago. how do i find out what's wrong and how do i fix it? our landlords are no help and we are on our own.