Question
QUESTION: My system worked fine for a few days, then one morning the backflow went off.  Do not know which zone it went off on.  Turned ssytem off and tested...everything seemed ok.  Thought it was a fluke.  Enabled system then backflow went off 2 days later. what could be the issue causing this?

ANSWER: Hey Steve,  I am sorry, but could you tell me what you mean by the backflow "went off".
I am sorry, but I am not sure what you mean, can you elaborate? Let me know, and I will answer the question, thanks and have a great day.

---------- FOLLOW-UP ----------

QUESTION: Sure, when the water flows out of the top of the system between the 2 valves.  I have a Wilkins 720A Pressure Vacuum Breaker.  For a few days the seal of the back flow part of the system is fine then it starts allowing water to flow out of it.

ANSWER: Hey Steve, does it only do it when you try to turn on a sprinkler system  valve? Or does it do it all the time? If it is doing it all the time without the system being on, then you need to rebuild the breaker with a new seat and plunger assembly. If it only does it when you try to turn a valve on, then it is either the pressure is too low (check the valve feeding the vacuum breaker to make sure it is turned on all the way), or there are too many heads on a line, or a break in the line, and too much water is being used by the system. The way the vacuum breaker works, is that the water pressure forces a plunger up onto a seat at the top of the vacuum breaker, if the water is shut off to the vacuum breaker, then there is no water pressure to force the plunger up, and it drops down, and what ever water is in the top of the vacuum breaker, will leak out the top, usually just for a few seconds. If you have the water turned on to the breaker, and it is leaking, then the plunger is not seating properly, and needs to be replaced. If it is leaking only when the system is turned on, then all the pressure is being used by the system, and there is not enough pressure to keep the plunger pushed up. Good luck and have a great day.

---------- FOLLOW-UP ----------

QUESTION: Happens then the system is on, not not all the time.  Only 4 heads in each zone.  System is set to turn on at 5 am and 2 pm.  It worked for the first 2 days then on the 3rd day we woke up and water was coming out of the top non stop.  I turned it off then reset everything thing and nothing leaking.  It ran for another day and a half and then my wife discovered water coming out top of it in the afternoon non stop.  When the water is coming out the the top, the sprinklers have finished there time running.  Not sure if it starts pouring out in the middle of the zones or at the end.   

This is the second year I've used the system.  Last year everything worked fine and I changed nothing this year.

Based on what you said, I'm guessing I have a break in the line in one of my zones some where.

Answer
Hey Steve, if the water continues pouring out, even after the system has shut off, then it still has to be an issue with the water pressure going to the vacuum breaker. Your pressure is also going to decrease if any other water is being used in the house, (washer, faucet, outside faucet, etc.). Where is the connected that feeds the vacuum breaker? It should be teed off of the main water line that feeds the house, and not from an outside faucet being fed through the house. Good luck and have a great day.