Central heating unit keeps turning on and off.

[Edricko]

It is not the thermostat. What can I do?

[Hiroshi]

If it is igniting for about ten seconds, then kicking off- look for a metal pin that sticks up in front of one of the burner tubes and should be engulfed by flame when the unit is heating.... this will be the "flame sensor." Scuff it clean with a piece of sandpaper or abrasive material... a small layer of ash will be insulating it from sensing the flame properly.

Be sure to shut-off the power so it doesn't try to barbeque your hand while you scuff the sensor!

Edited December 12, 2016 by Hiroshi