How to replace a commercial flush valve

Not sure about your brand but many toilets have a flapper valve inside the tank which needs adjusting or replacing. Try this U tube link
How To Repair Mansfield Toilet

If there is water still running into the toilet bowl, there is a problem with your flapper or flush valve. The most common problem, and least expensive to fix, is the flapper has gone bad and is allowing water to escape past it. Replace the flapper and the water should stop running. If not, it is possible the flush valve or one of the seals holding it to the tank has gone bad and needs replaced. Try replacing the whole flush valve. They come in a kit that includes the valve, flapper, and seals.

Likely corroded or warn out. In most cases replace the fill valve. I prefer Lavelle replacement fill valves. If toilet is an old 3.5 gallon or higher model or an early water saver, consider replacing the toilet with a latest generation name brand 1.6 or 1.28 flush model with a glazed trapway.

The flapper at the bottom of the tank is leaking and needs replacement.

replace the whole valve. It's cheap and easy to do. Probably you can install a universal valve. Look on e-bay or amozon

I’m happy to help further over the phone at https://www.6ya.com/expert/robert_24775b73ca70da93

either the fill valve is running and water is draining into the bowl via the overflow tube in the tank or the flapper is bad (or foreign matter) and it is allowing water to escape into the bowl through the flush valve slowly...causing the tank to drain and the fill valve to run every few minutes or so. start by inspecting/cleaning or replacing the flapper and hopefully that will do it because a one piece toilet flush valve needs a special wrench,to remove it, that you use with a ratchet. If you buy a new flush valve, it comes with the wrench (glorified piece of plastic) and is not too difficult to get the flush valve out. you can get a replacement at http://www.plumbingpartsdepot.com/ They do mail order, too. All you need is the toilet type - a four digit number embossed in the tank starting with a 2. hope this helps but if you need anything else just ask:)

How to Troubleshoot a Flushometer

A flushometer consists of a metal pipe extending from the back of a toilet with a slender handle on the side that is used to flush a toilet. This type of flush valve is commonly used for toilets in commercial facilities to provide a durable and accurate flush delivery system. If the flushometer does not work properly, troubleshoot it and perform minor repairs. Common issues are often resolved quickly. If troubleshooting does not correct the problem, call a plumber for repairs.

Does Not Flush

1 Inspect the handle assembly. A broken handle or assembly will prevent flushing. If damaged, unscrew and remove the handle assembly. Replace the handle or repair it with a handle repair kit

2 Open the main water supply valve to turn the water on fully. The water supply is normally turned on, but check to make sure it is turned on fully and has not been turned off inadvertently

3 Remove the flushometer's CP cover, the round cap on the very top of the pipe extending from the toilet. Then remove the inside cover directly underneath the cap. Inspect the relief valve. Replace it if it is visibly damaged.

Short Flush

1 Remove the CP cover and inside cover. The CP cover is located on the very top of the pipe extending from the back of the toilet. The inside cover is underneath the CP cover and the diaphragm assembly is located beneath the inside cover. Remove and inspect the diaphragm assembly. A damaged diaphragm assembly can cause a short and incomplete flush. Replace it if it is visibly damaged.

2 Replace or repair the handle assembly. A damaged handle can result in a short flush. If damaged, unscrew and remove the handle assembly. Replace the handle or repair it using a handle repair kit.

3 Remove the CP cover and inside cover to remove the diaphragm assembly. If a low consumption diaphragm is installed on a water-saver fixture or a urinal diaphragm is installed on a toilet fixture, replace it with an appropriate diaphragm.

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A fluid master should be universal and as long as it will allow the water to reach set mark on overflow pipe.

It sound like you have debris caught in the fill valve. Remove the top where the washer is and put your hand over it and slowly turn the water on to flush the fill valve. Replace the washer with a new one and then replace the top.

If you have the old ball and **** style, replaceing the diaphram is harder so I would recommend replacing it with a fluidmaster fill valve. Hope this helps.