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20 years old. Original installation. Hunter controller. 5 of 6 zones valved with sprinklers.

All five zones do not turn on from controller.

All five zones do turn on from valve using screwdriver on solenoid.

Two of five valves flooded the valve housing while running in manual mode.

Do I replace all five solenoids?

Do I clean all five solenoids, reassemble, try again?

Need sprinklers as I just burned / killed my beautiful grass with some faulty chemistry / application.

I would guess you will need to replace the two bad valves if they are leaking from the valve itself, of it is the solenoids leaking just replace those two.

If you are lucky enough to find the same valves in a store, you can prob just replace the top part without having to replace the entire valve, as in without having to cut and re-plumb the piping connections to the valves.

With the controller not working, I had a glorious dirt dauber nest in mine. Just replaced it, never mind trying to clean that shit out. And then make sure you seal up any access to inside the box! LOL.

Oh, and my experience had been water in the box doesn't keep the valves from operating.

 
Before replacing the two that are leaking, I would turn off the water supply, and carefully take the top off, keeping track of which parts go in which order. There is a screen filter in there that can get pretty clogged up, especially if you have hard water. I only have two, but I clean them about every 3 years.

What they said.

I’d tear apart each valve and clean them. Them try it again.
Next is the wiring....do you have a meter where you can check each valve/zone.

But it might be in the control box....or at the connections in the valves/zones...after 20 years the connections Amy be corroded, might be easy to strip and re-wirenut/connect the wiring

Valves are cheap, it really depends on how long the system has been dormant. We did some of the typical fixes on a system with similar age and years of being unused, eventually after getting the valves to run they began to fail as the problems from age began to take over.

Same for the sprinklers, fix one chase the leak, fix another find another cracked line. Typical stuff.

Even if the controller works, consider updating to a Rachio, it’s fully programmable from a smart phone app, ties to your local weather station to adjust for rain, a good upgrade well worth it,