Toilets, Sinks, Showers, Tubs and Disposals - Fluidmaster not functioning properly

Toilet installed about 5 years ago with Fluidmaster 400A. Recently it stopped filling thru refill tube after flushing. (Water does trickle [leaks and drips] into tank from valve top and shut-off arm and will re-fill tank in 5-8 min. But nothing comes thru refill tube. HOWEVER, IF I TURN OFF WATER LINE AND IMMEDIATELY TURN BACK ON - WATER WILL FLOW THRU REFILL TUBE AS IT SHOULD. THIS ONLY HAPPENS IF YOU TURN OFF/THEN TURN ON WATER LINE. What goes ?
I don't mind putting in a new Fluidmaster, but I would really like to understand what is happening here? (By the way, I have removed top cap and flushed out inside of valve body and also checked washer in the top cap and found no contamination or visual problems). Also, there is ALWAYS full water pressure at the top cap. AGAIN, WATER FLOWS THRU REFILL TUBE ONLY IF YOU TURN WATER LINE OFF/THEN ON !!! Please help as this is driving me buggy !!!

Dirt sounds like the culprit; when you turn the water off you might be causing the dirt to go another direction, then after filling it goes back to where it once was.



I would replace the seal inside of the fill valve first, and see if this corrects the problem, but most likely replacement is your best option.

Where do I find the seal inside the fill valve ? Not sure how I would remove without removing the entire valve and valve body ? Can I buy this seal without having to buy the entire Fluidmaster ?

The link below is for troubleshooting the Fluidmaster 400A

http://www.toiletology.com/troubles.shtml

Rainbird, -thanks, that was a great link. You can also follow it to the Fluidmaster site which is very informative. :cool:

Do it Right - Do it once.

Thank you all for your replies and the link to Fluidmaster - that will be most helpful in the future. Problem solved by replacing rubber seal in top cap of Fluidmaster. Also discovered that you can purchase this seal made by Fluidmaster from any Ace or True Value Hardware store. Only concern I have is that on the package for this seal, Fluidmaster says that if unit is 5 years old you should replace fill valve or there could be flooding problems - scary words - any truth here or are they just trying to increase revenue ? Also, I still can't understand how or why this seal was preventing water flow until water supply were turned off/then on ! - and that's after reading how the fluidmaster valve works as written on the fluidmaster.com site