Replacing the bulb or quartz sleeve in a pond UV clarifier

In brief

• Always switch off the power and unplug the unit before opening it.
• Check the brand, exact model and wattage on the rating plate before ordering.
• Replace the bulb at the intervals specified by the manufacturer, even if it still lights up.
• The quartz sleeve can be cleaned; replace it if it is cracked, scratched or remains cloudy.
• Replace the O-ring if it is flattened, hardened or cracked.

Replacing the bulb or quartz sleeve in a pond UV-C clarifier usually takes very little time. Switch off the power, isolate the unit, open the housing according to the instructions, replace the part and check for leaks before switching it back on. The most important step comes first: ordering the right part for your exact model.

Bulb, quartz sleeve, seal: what does each part do?

• The UV-C bulb emits radiation that acts on algae suspended in the water. It wears out over time: it may still light up even after it has lost its effectiveness.
• The quartz sleeve is the transparent glass tube that protects the bulb from the water. If it is dirty or covered in limescale, the radiation cannot pass through properly.
• The O-ring seals the gap between the quartz sleeve and the housing. A worn seal can cause leaks and let water in.

To find out when to replace the bulb, read our article on how often to replace a UV lamp.

Before you start: identify the right part

1. Check the unit’s brand and exact model on the rating plate.
2. Note the wattage.
3. If possible, remove the old bulb and note its part number, length and base type.
4. For the quartz sleeve, note its length and diameter, or, better still, the manufacturer’s part number.

A bulb with the same wattage but a different base will not fit. If in doubt, send us the brand, model and a photo of the rating plate.

How to replace the UV-C bulb, step by step

1. Switch off the power and unplug the UV unit. Unplug the pump as well.
2. Let the bulb cool for a few minutes.
3. If the unit is installed in-line, close the valves or isolate it to prevent water from flowing out.
4. Open the housing according to the instructions: the cap, nut or cover, depending on the model.
5. Remove the old bulb from its socket without forcing it.
6. Handle the new bulb with a clean cloth or gloves. Avoid leaving fingerprints on the glass.
7. Insert it into the socket until it stops.
8. Check the seal, then close the housing.
9. Restore the water supply, check for leaks, then plug the unit back in.
10. Check that the indicator light comes on.

Safety: Never look at a UV-C bulb when it is lit outside its housing. The radiation is harmful to your eyes and skin.

How to clean or replace the quartz sleeve, step by step

1. Switch off the power, isolate and drain the unit.
2. Remove the bulb as described above.
3. Unscrew the nut or ring holding the quartz sleeve in place.
4. Gently remove the quartz sleeve, holding it by the ends.
5. Inspect it in the light. White or brown deposits can be cleaned off. Replace it if it is cracked, deeply scratched or still cloudy after cleaning.
6. To clean it, use a soft cloth and a limescale cleaner. Do not use anything abrasive.
7. Rinse with clean water and dry.
8. Replace the O-ring if it shows signs of wear.
9. Refit the quartz sleeve, hand-tighten without overtightening, then reinstall the bulb.
10. Restore the water supply and check for leaks before plugging the unit back in.

Clean the quartz sleeve whenever you replace the bulb. Both tasks can be done at the same time.

Common mistakes to avoid

• Opening the unit while it is powered on.
• Ordering a bulb based on wattage alone, without checking the base and length.
• Overtightening the quartz sleeve ring, which could crack the glass.
• Reusing a compressed seal.
• Plugging the unit back in without checking for leaks.
• Assuming a bulb works because it lights up. Visible light does not prove that the bulb is still emitting enough UV-C radiation.

Is the water still green after replacing the bulb?

A new bulb is not always enough. Check the flow rate through the UV unit, the cleanliness of the quartz sleeve, the filtration and the nutrient levels. Our guide to green pond water despite using a UV lamp explains what to check. Also give the system a few days to work: the water will not clear instantly.

Where to find replacement parts

• Replacement UV-C bulbs for ponds
• Replacement quartz sleeves for UV units
• O-rings for UV units and pumps
• Quartz sleeve and pump cleaners

If your unit is too old or replacement parts are no longer available, browse our pond UV-C units.

Need help finding the right part?

Send us the brand, exact model and a photo of the rating plate on your UV unit. We’ll tell you which bulb, quartz sleeve and seal are compatible.

Telephone: +32 10 86 03 54 – Email: support@foudebassin.com. Replies on business days.

Frequently asked questions

My bulb still lights up. Should I replace it?

Yes, if it has exceeded the service life specified by the manufacturer. A UV-C bulb can still light up even after it has lost much of its effectiveness.

Can I fit a more powerful bulb in my unit?

No. The ballast and housing are designed for a specific wattage and size. Use only a bulb that is compatible with your model.

The quartz sleeve broke while I was removing it. What should I do?

Do not refill the unit. Order a quartz sleeve with the same part number and a new seal. Send us the exact model to make sure the parts are compatible.

Should I switch off the UV when adding bacteria?

Some bacterial products require you to switch off the UV for a specified period. Follow the instructions on the label of the product you are using.