If I turn the thermostat up more than a few degrees, it shuts off after increasing one or two degrees and won't come back on. I can either turn the breaker off/on or, I just figured out, I can turn the thermstat down until it clicks and then back up again and it will come back on. But, it turns off again later and still doesn't meet the setting. The thermostat is new. The heater is on the roof, and it's gas.

Thank you,

Meg

Brand of heater?
Model number of heater?

Brand of thermostat?
Model number of thermostat?

Sounds like it is overheating, this is only one of several possibilities.

https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313-2.html#post269282