I have tried two brand new fluidmaster toilet valves. It is very inconsistent. Sometimes it doesn't allow the tank to fill, sometimes the floater does not engage causing perpetual flowing of water, sometimes it works fine, but never more than 2 flushes in a row. Any suggestions?
1 The float must not be near any obstructions.. Sometimes the valve body was rotated too near the rear of the tank, causing the float to graze and hangup.
2 Another problem can be the refill hose is cut too short, causing the valve to bind.
3 Another issue is not extending the valve tube (it rotates, getting longer or shorter, affecting the tank level.
4 Also check under the valve top, for bits of rust/pipe crud, which can cause very flaky operation. Be sure to turn the water off for this one...