An in-line unit has no cartridge and no media to swap on a fixed count. It has two parts that wear — the lamp, whose output falls gradually, and the quartz sleeve, which fouls — plus two things upstream and downstream of it that are not part of the unit at all. The interval that matters most is the sleeve's, and it is set by water quality rather than by the calendar. A unit whose lamp still lights and whose indicator still reads green can be doing very little; the service schedule explains both ways that happens.
Servicing a UV stage is mostly about knowing which of four things has changed. Three of them are not part of the unit at all, which is why a maintenance plan that covers only the product is a plan with three holes in it.
The four items in the chain and who decides each interval, the conditions at an address that shorten or lengthen the sleeve interval, and what the 15,000-hour design rating is and is not. Written for whoever keeps the log, not for whoever wrote the specification.
| Item | What happens to it | What sets the interval |
|---|---|---|
| Lamp (UVC-LED assembly) | Output falls gradually over service. The lamp continues to light, so the failure is invisible without reference to elapsed hours. | The manufacturer's design rating, adjusted for drive current and thermal conditions. This is the one interval that is a clock. |
| Quartz sleeve | Scale, iron and organic film deposit on the surface the light has to cross. Deposits absorb ultraviolet light, so transmission falls while everything else looks normal. | Water quality — hardness, iron and turbidity — plus whatever upstream events release sediment. This is the interval that varies most between installations. |
| Upstream filter stages | They load up and pass what they can no longer hold. The UV stage inherits the result. | The host system's own schedule. A pre-filter run past its change interval is the most common way a UV unit ends up working on water outside its conditions of use. |
| Tank and tubing downstream | Wetted surfaces can harbour growth. The unit protects the water passing it, not the surfaces after it. | Visual inspection and the condition of what is found. Keep the run after the unit short; clean or replace where growth appears. |
Two addresses with the same unit can need the sleeve inspected years apart: one on soft, clear water and one on hard water with iron present are not the same service case. A single printed interval would be a guess presented as a schedule, so the interval is set from what the feed water actually is — which is also why the feed-water limits are the first page worth reading after this one.
| Condition at this address | Effect on the interval | What to do about it |
|---|---|---|
| Hardness well inside the limit | Longest interval of the cases here. | Inspect at the first scheduled service and extend from what is found, rather than assuming a default. |
| Hardness near the published limit | Measurably shorter. Scale builds on the sleeve as it does on a faucet aerator. | Inspect earlier than the first scheduled service and set the interval from the inspection. Consider scale control upstream. |
| Iron present, even below the limit | Shorter and more variable. Iron deposits are coloured films that absorb the light. | Treat iron as the primary fouling risk at this address and inspect the sleeve before anything else when performance is questioned. |
| Turbidity near the limit, or a known sediment event | Interval shortens sharply after the event. | Inspect after any upstream event that dislodged sediment — a well recharge, a main repair, a filter change carried out carelessly. |
| Continuous or high duty cycle | Both the sleeve deposit and the lamp hours accumulate faster in real terms. | Express the lamp interval in operating hours rather than months, and keep the log accordingly. |
It is
A manufacturer's design rating for the LED assembly, at a stated minimum output proportion. It is also a planning figure for how the lamp interval should be expressed — in operating hours rather than in months.
It is not
A measured lifetime. No qualification report is held and none is implied. It is not a guarantee of hours in service either: drive current, thermal conditions and duty cycle all move the real figure.
No lifetime test evidence is held for the LED assembly. Where a market requires one, the qualification has to run under that market's own programme — the figure on this site is a design rating and is not presented as anything else. The same rule governs the site's approach to dose: no figure without its test conditions.
For a service question, send the feed water result and how long the unit has been in service. For a replacement, send the model number from the label and the quantity — the lamp and sleeve are matched to the model.
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