Why do some of my sprinkler heads leak when the system is on

There were other systems as well like Halon, which is no longer used and CO2 systems, which I am not even sure if they still use either since they now have a water fog system that I am told works very well. Maybe I should investigate and see what they have come up with since I retired.

If water pressure is over minimum recommended rate, your replacement sprinkler head shouldn't leak; it it's leaking probably because it is of a very bad quality. If it's new, return it to the shop where you bought it and clim your warranty right

Either the pressure has gone down due to a leak or the heads have gotten dirty inside and need to be cleaned out so they again pop out fully.

Water will continue to run back down the hills to the lowest Heads and Some water will come out.It will stop once the water in the lines has Drained out.

It could be the shutoff valve (debris in stem tip), but most likely cause is that the sprinkler is the lowest point in that line and, after shutoff, the water in the system is draining to the lowest point.

if this is an older sprinkler ,it may just be worn.usually the leak is around the white plastic surrounding the popup shaft.in this event the cap needs to be replaced.

THERE TWO CAUSES THAT I KNOW OF: 1. YOUR FAUCETS ARE PRESSURE SEALING MEANING: THEY NEED A MINIMUM PRESSURE TO SEAL MOST LIKELY 25psi, YOUR SPRINKLER SYSTEM IS STARVING THE ENTIRE SYSTEM OF PRESSURE WHICH ALLOWS YOUR FAUCETS TO LOOSE THEIR SEAL. SOLUTION:REPLACE FAUCETS WITH SPRING SEAT SEALING FAUCETS. 2. YOU HAVE A WATER LEAK IN YOUR MAIN WATER LINE AND THE FAUCETS ARE LEAKING AIR BACK INTO THE MAIN LINE WHEN THE SPRINKLERS ARE OFF AND WATER INTO THE SINK WHEN THE SPRINKLERS ARE ON... THIS SCENARIO IS UNLIKELY AND YOU WOULD HAVE OTHER PROBLEMS SUCH AS AIR IN THE LINES AND THE FAUCETS WOULD LEAK WHEN YOU TURNED ON THE SHOWER AS WELL AS THE SPRINKLER SYSTEM.

The lowest sprinkler head usually leaks until all the water is out of the system. The valve that controls the sprinkler system has a vaccum breaker valve on it. When there is no pressure from the water main the vaccum valve opens allowing the sprinklers to leak water so the house water won't get contaminated from the grass and dirt in your yard.