An ultraviolet controller has very little to tell you and it matters a great deal. Most units signal three things: the lamp has failed, the lamp is due, or the measured intensity has dropped. Those are not the same fault, and the most dangerous condition is the one that produces no signal at all, which is why knowing what the controller does and does not monitor is part of owning one.
Lamp failure against lamp due
A lamp failure alarm means the controller has lost the electrical signature of a working lamp: the lamp has failed, the connector has worked loose, or the ballast has died. Check the connector first, since it is free. A lamp due reminder is a timer counting down from the last reset and knows nothing about the lamp's actual condition, which is why resetting it without changing the lamp is a way of turning a maintenance system into a decoration. Change the lamp, then reset.
Low intensity, which is the useful alarm
Units with a sensor measure how much ultraviolet is actually reaching the water through the quartz sleeve, and a low intensity warning has three causes in order of likelihood: a fouled sleeve, an ageing lamp, and a fouled sensor window. Clean the sleeve and the sensor at the same visit, since both foul from the same water. If intensity is still low with a clean sleeve and a fresh lamp, the water itself is the problem: iron, turbidity or dissolved organics are absorbing the light, and the pretreatment needs attention rather than the lamp.
The failure that produces no alarm
A unit without an intensity sensor cannot tell you the dose has fallen. The lamp glows, the controller is content, and the sleeve slowly films over or the lamp ages past its useful output. Nothing changes that a household would notice. That is the strongest argument for a sensor, and for a solenoid valve that closes the supply on failure where nobody would act on an alarm. It is also why the annual lamp change is a rule rather than a suggestion.
Power, flow and the things around it
A controller on a circuit that trips leaves the lamp off while the house keeps drawing water, so a dedicated and reliable supply matters more than it seems. Check that flow has not risen beyond the unit's rating, which happens when a household adds fixtures or when a pump is changed. The EPA notes private wells are not federally regulated under the Safe Drinking Water Act, so after any fault the only way to confirm the water is right is to test it. Our uv bulb guide covers the annual service.
Questions people ask about uv light system
What is the difference between a lamp failure and a lamp due alarm?
Failure means the controller has lost a working lamp's signature. Due is a timer that knows nothing about the lamp's real condition.
The low intensity alarm is on. What do I check?
The quartz sleeve first, then the lamp age, then the sensor window. If all are clean and fresh, the water itself is absorbing the light.
Can I reset the reminder without changing the lamp?
You can, and it turns the maintenance system into a decoration. Output fades regardless of what the timer says.
What if there is no alarm but I am unsure?
A unit without an intensity sensor cannot report a fallen dose. Test the treated water, and consider adding a sensor or a shut off solenoid.