heater mats under tanks

A clamp-on ammeter will tell if the current flow is within specs. Often there is a thermostat right at the heating element. Depending on temperature you may need to place an ice pack right on the thermostat to close the switch.

There is nothing to tell you the pads are on. The light being on just tells you power is available to the pads.

dblr wrote:
They work very much like a water bed heater and work off of a thermostat, we were told even if ours are turned on unless the temperature drops to around 40 the tank heater will not come on

Most, do have an internal tstat in the pad. The way I test, is to take a can of PC air and turn upside down to freeze the area where the wires enter the pad(where the tstat is). I then wait a few minutes and shoot the actual pad with an IR thermometer to make sure it is heating. Doug

They work very much like a water bed heater and work off of a thermostat, we were told even if ours are turned on unless the temperature drops to around 40 the tank heater will not come on