Well water system - chlorine tank remains full
I have a chlorine injection water treatment system for our well water. The chlorine tank has a dip hose with a filter on the submersed end. This hose runs to an injection pump. There is a dial on the pump for setting the dose to be injected per cycle of the pump, which is triggered by a water flow valve. The injector also has a valve to prevent back-pressure from forcing water into the pump and conceivably into the chlorine tank

But wait, there's more.

The now-chlorine-infused water should then enter a settling tank, to remove reactants from the chlorine and any sediment. The next tank should be a carbon filter to remove left-over chlorine. If you have a water conditioner/softener, that's the next stop on its travel to your plumbing/dispensation within your residence.

It's unlikely that the dip hose filter is clogged.

It's possible a tech turned the dose knob and reduced the volume to zero. There's no set figure for the dose; it's established over time and testing of the chlorine level at the use point.

The injector valve can easily become clogged, especially if you have a high iron content. My valve is called a duckbill and the iron deposits fill the beak, causing it to stick open, allowing more iron into the opening, eventually filling and clogging the valve. Local suppliers will carry the valves, but online is about one-quarter to one-sixth the cost. I believe I paid five dollars each, possibly less for what the locals charge about thirty-five bucks!

After the injection valve, there's very little to go wrong, unless your flow valve is stuck in the off-position. That's very unlikely, as the flow valve would prevent water flow to the house. It's more common to have it stick in the on position, over-dosing the water with chlorine, easily detected by taste and smell.

The injection pump typically dislikes to be run dry and will sometimes not prime when the chlorine tank is refilled. There should be a priming knob/valve atop the pump. When turned 90 degrees to detent, the air in the line is forced out. You should have a discharge/priming hose that returns to the chlorine tank and can watch the pulses from the pump when the priming is complete.

It's a high maintenance system if something goes awry, but when it's running well, it's great to have clean iron-free water. If you discover that it's the injection valve, buy a quantity and replace them on a calendar basis, rather than on a failure basis. I get three months between changes and have no more injection lapses.

Other types of systems can be found at the clean water store web site which effectively changes the method that triggers/measures/dispenses the chlorine. The above description is one of those at the site. The image below comes from this site.