Turn it off and wait until it is 10 or more degrees cooler than the setting, see if it runs longer, if it does then look for drafts (hot or cold) that could be influencing the thermostat. If it makes no difference then there is likely a control circuit problem.
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Turn it off and wait until it is 10 or more degrees cooler than the setting, see if it runs longer, if it does then look for drafts (hot or cold) that could be influencing the thermostat. If it makes no difference then there is likely a control circuit problem.