I installed a new water heater and the pop off or pressure valve is leaking a small stream of water. Can this be stopped without installing a new valve?

Not unless the water is at a very high tempature, higher than the pop off valve is set at. If it was like this when you installed it I think the valve is bad.

Sometimes you can open and close the relief valve a couple of times and then it seals like its supposed to. Try that. I've had success doing that on a lot of them.

Bruce in L.A.

No you must change the valve or it will leak al the time this has a pressure spring and it got damaged meaby by frost so change it it drip down into hot press and then rust will destroy clothes in press

Hopefully you replaced the pressure/temp. relief valve when you installed the new water heater. You really should, they don't cost that much. The valve is leaking for one of three reasons; the temp. is too high, the pressure is too high or the relief valve is defective. You first need to determine which it is before you can remedy the problem. Check the temp. with a thermometer at a hot-water spigot outlet and check the pressure with a gauge attached to a hose bib. If they check out OK (below the relief valve ratings) you need to replace the relief valve.