Hi, Twice now in the last 2 days my heater won't turn on. If I turn it off and then back on it will start to run. Does anyone know what might be causing this to happen?

More info needed,, is it elect or gas,, anymore details would help

It is a rheem gas furnace. It will run for a few hours and then you will notice it starts to get chilly. If I turn the digital thermostat off and then back on it will run again for a few hours before it stops working again. Could it be a problem with the thermostat upstairs or the furnace filter?

If it's a 90% furnace(vented with PVC pipe) you may have a froze or restricted condensate drain. If water backs up in the drain line to the trap on the furnace it will open the pressure switch and shut the system down, check for kinks in the rubber lines going to the condensation trap inside the furnace. Rheem has had a few problems with the rubber drain lines inside the unit with the older 90% furnace.