My house initially had low water pressure at only 40 PSI. I had a plumber replace the pressure regulator valve which brought the pressure up to 65 PSI. Ever since the new valve was installed and the pressure was increased, I am experiencing water hammer behind the refrigerator every time the sprinkling system switches on (the fridge has a water dispenser and ice maker). This only happens when the sprinkling system switches on. Is this a problem that I need to worry about?

Possibly related or not, one quadrant of my sprinkling system suddenly has no pressure and very little water comes out, indicating there is now a major leak somewhere. This began at the same time that the pressure valve was replaced and the water pressure increased. The higher water pressure has probably blown an already weak pipe or joint in the sprinkling system somewhere underground. There is no wet spot or depression in the ground to identify where the break is. How do I locate where the break is so I can dig and repair it?

 

Leak in sprinkler is usually easy to find. Just turn on zone that leaks and look for the wet spot. If underground may have to run for a few minutes. Plunbers should be in soon about water hammer.

 

Do you have an expansion tank on your interior plumbing? Like this:
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As your water heater heats water, the water expands and can cause higher pressure in the house. Without an expansion tank, the pressure can build up well over the 65psi that you have normally.

Does it do it only in the morning when the sprinklers go on? Try turning on a faucet for a moment before the sprinkler goes on - does it hammer still?

 

I doubt it's a leak. More likely would be something is caught in the valve and keeping it from opening. Possibly crud from the reducing valve replacement.

See if you can open the valve manually.

An expansion tank or large air chamber would reduce/eliminate the air hammer problem.