La Marzocco Coffee Machine Sight Glass Leaking — How to Replace It
The sight glass on your La Marzocco espresso machine lets you see the water level inside the steam boiler at a glance. Over time, the sight glass tube or its fittings can develop a leak — you'll notice water dripping from the side of the machine, often from around the glass tube or its upper and lower fittings. A leaking sight glass needs to be replaced promptly: continued operation with a leak can cause water damage inside the machine and makes it impossible to accurately monitor boiler water level.
The good news is this is a straightforward repair that most technicians and confident DIYers can complete with basic tools. Follow the steps below carefully.
⚠️ Safety Warning
The steam boiler operates at high temperature and pressure. Never attempt to remove the sight glass while the machine is hot or pressurised. Follow the shutdown and depressurisation steps below exactly before touching any fittings.
What You'll Need
- Replacement La Marzocco sight glass (LML120/C — see product below)
- Adjustable spanner or correct size open-ended spanner
- PTFE tape
- Towels or a tray to catch residual water
- Phillips screwdriver (for panel removal)
Step-by-Step: How to Replace the Sight Glass
Step 1 — Turn Off the Machine and Release Steam Pressure
Switch the machine off at the main power switch. Do not unplug it yet — leave it switched off at the panel. Open the steam wand fully to begin releasing pressure from the steam boiler. Allow all steam to vent completely until no more steam exits the wand. This may take several minutes. Once steam has stopped, close the steam wand.
💡 Tip: Do not rush this step. Even after the machine appears to have stopped steaming, residual pressure can remain in the boiler. Wait until the steam wand produces only cool air or nothing at all before proceeding.
Step 2 — Unplug the Machine and Allow It to Cool
Once all steam pressure has been released, unplug the machine from the wall. Allow the machine to cool for at least 30–45 minutes before opening any panels or touching the boiler or fittings. The boiler and surrounding components retain heat long after the machine is switched off.
Step 3 — Remove the Top and Side Panels
With the machine fully cool and unplugged, remove the top panel and the relevant side panel to access the steam boiler and sight glass. On most La Marzocco machines the panels are secured with Phillips head screws — keep all screws in a safe place. Set the panels aside carefully to avoid scratching the stainless steel.
Step 4 — Drain the Steam Boiler
Before removing the sight glass, the steam boiler must be drained. Locate the boiler drain valve (typically at the base of the boiler) and open it slowly to drain the remaining water from the boiler into a tray or bucket. Allow the boiler to drain completely before proceeding. Confirm the boiler is empty by checking that no water flows when the drain is fully open.
💡 Tip: Place towels around the base of the boiler before draining — some residual water will spill when you disconnect the sight glass fittings even after draining.
Step 5 — Remove the Old Sight Glass
With the boiler fully drained, use a spanner to carefully loosen and remove the upper and lower sight glass fittings. Support the glass tube as you loosen the fittings — do not let it fall. Remove the old sight glass tube and fittings completely. Inspect the boiler ports for any scale, corrosion, or debris and clean if necessary before fitting the new glass.
Step 6 — Fit the New Sight Glass
Apply 2–3 wraps of PTFE tape to the threaded fittings of the new sight glass assembly. Thread the fittings into the boiler ports by hand first, then tighten firmly with a spanner. Do not overtighten — the fittings only need to be snug and leak-free. Ensure the glass tube is seated correctly and the fittings are aligned before fully tightening.
Step 7 — Reassemble and Test
- Close the boiler drain valve
- Refit the side and top panels
- Plug the machine back in and power it on
- Allow the machine to fill and heat to operating temperature
- Monitor the sight glass and fittings closely during the first heat-up for any signs of leaking
- If no leaks are present after reaching operating temperature, the repair is complete
⚠️ If the new sight glass leaks: Switch the machine off immediately, release pressure via the steam wand, and allow to cool before re-tightening the fittings. Do not attempt to tighten fittings while the machine is hot or pressurised.
🛒 Shop La Marzocco Sight Glass
This is the correct complete sight glass assembly for La Marzocco espresso machines:
Frequently Asked Questions
How do I know if the sight glass is leaking or if it's a different component?
Sight glass leaks typically appear as a slow drip or weep from the glass tube itself or from the upper or lower fittings where the tube connects to the boiler. If water is coming from elsewhere on the machine, the source may be a different component. Contact us if you're unsure of the leak source.
Can I run the machine with a leaking sight glass?
No — a leaking sight glass should be repaired before the machine is used again. Continued operation risks water damage to internal components and makes it impossible to accurately monitor boiler water level, which can lead to the machine running dry.
Does this sight glass fit all La Marzocco models?
The LML120/C sight glass fits a range of La Marzocco commercial and prosumer machines. Contact us with your model name and serial number to confirm compatibility before ordering.
Do I need to replace the fittings as well as the glass tube?
The LML120/C is a complete assembly — it includes the glass tube and fittings. If your existing fittings are corroded or damaged, replacing the complete assembly is the recommended approach.
Not Comfortable Doing This Yourself? Book a Service.
Boiler work requires care and the right tools. If you'd prefer a technician to handle the repair, our team services La Marzocco machines across South Sydney, Eastern Suburbs, Sutherland Shire, and Georges River.
Need a technician to replace your sight glass?
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