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I have a Rain Bird RC-7A controller. Recently I connected a pilot light (24 volt bulb) to the terminals for the master valve (Asco solenoid valve 8210G009). A few hours after the regular watering cycle is completed, the controller sends one or more electrical pulses to the master valve. This causes the valve to suddenly open and close, which results in a horrendous water hammering in the supply pipe coming from the basement to the vacuum breaker system. Disconnecting the pilot light stops the problem. Any ideas about what's going on here?

Quoted from "Wet_Boots"

Sounds very much like Operator Error to me - how many zones are in the system?

OK, I'll bite - - what kind of error might it be? I've checked it out as much as I can, and I know it sounds absolutely ridiculous. There are seven zones on the controller, but only five are in use.

Quoted from "Wet_Boots"

You should take the lamp and install it at the master valve, in parallel with the solenoid,

That's exactly the way I had it when the trouble occurred. (The lamp is the size of a flashlight bulb, with bayonet base.)

Wet_Boots: Thank you for your kind consideration of my problem. I'm embarrassed to now report that the aforementioned pilot light isn't related to the problem after all, as the electrical pulses to the master valve have now returned in its absence - - and they're still resulting in the serious water-hammering I described, a few hours after completion of the regular watering cycle. So that would seem to bring the cause back to the RC-7A itself, as I cannot think of any other culprit. I do apologize for my original "diagnosis" about the pilot lamp, and I remain totally mystified about what's going on. Meanwhile I'm afraid the water-hammering threatens the integrity of the pipes involved. I very much apologize for leading you down the rabbit trail of the pilot light, and will be grateful for any further wisdom you may wish to offer if I've not exhausted your gracious patience by this time.

Perhaps I'm not "getting it," but do you mean to connect the wires from three controller zones all to one zone valve? How would that work to alleviate my problem?