I have an older gas heat only boiler with millivolt system.I installed a new thermocouple and new thermostat(2 wires red and white).Thermostat is battery powered.Everthing works fine,but 24 hours later the ciculator pump will come on but the burner does not ignite.The same thing happens if I turn the switch off and turn it back on.If I remove the batteries and put them back in it works fine again until the next day.Any ideas what could be the problem?