If it is a richdel valve and it is fairly old did it have an o'ring in the bonnet of the valve? Meaning this: When you unscrewed the solenoid was there an o'ring in the top of the valve?
If there was and you installed a new solenoid with an o'ring already installed inside of the actual solenoid, you have effectively doubled up the o'rings....causing the solenoid pin to not seal, causing the valve to continuously run.
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