[hvac1000]

My gas would turn on for four seconds then off then on again for four for seconds then stay off for two minutes and then the same thing I cleaned the flame sensor on the unit with sand paper as suggested above and it worked!! Thanks very much!!

Your welcome

[edware]

Check the flame sense probe insulation. It is a cloth insulation and if it gets wet, will conduct enough to attenuate the flame sense signal.
A good idea is to insulate the flame sense lead with heatshrink tubing to prevent moisture from affecting it.
In many cases removing the sensor and replacing it again is enough to allow some of the moisture to dry out and make the sensor work again.
Cleaning the sensor with emery paper is likely to have a negligible effect.