Note: Like another user's query, our bowl fills okay, but the tank refills very slowly - takes 15-20 minutes. We can't detect any leaks. I've adjusted the water valve. I've put a brick in the tank to raise the water level per someone's suggestion. I can't detect any issues with the flush handle or any of the components in the tank. However, understand: Both my husband and I are totally UNKNOWLEDGEABLE about this sort of thing. We managed to change the flush valve a few months ago, and I think he changed the entire interior mechanism as well - but beyond that, we're helpless! We simply can't afford a plumber(still paying off a $10,000 water re-route from two years ago). Ideas?
Assuming the old valve was replaced for just not shutting off & this is only happening after the new toilet valve went in. Then yes, it's debris in the line that ruined the new valve, likely from operating the shut-off valve. The toilet valve should be replaced again after flushing the supply line while opening & closing the shut-off valve to make sure all debris is gone.
You may want to turn the house main down a bit, you just want to flush the line (turn on a faucet closest to the main) & turn the main mostly closed so the faucet drops its flow to half but not less, you still want to scrub out the debris pretty good.
***** THE MAIN may also have debris so remove the faucet's aerator & operate the main until water runs clear.*****