La Marzocco Coffee Machine Won't Stop Running — How to Replace the Flowmeter Cap
Your La Marzocco espresso machine starts a shot and just keeps going — it won't stop at the programmed volume. The pump runs continuously, the coffee overflows the cup, and the only way to stop it is to press the button manually. This is a classic sign of a flowmeter fault, and in most cases the cause is a failed or worn flowmeter cap.
The flowmeter cap houses the magnetic impeller that spins as water flows through it. The control board counts the pulses from the spinning impeller to measure the shot volume. When the cap fails — due to a worn O-ring, a cracked cap body, or a seized impeller — the board can't count pulses correctly and the machine either runs non-stop or stops too early.
⚠️ Safety First
Always turn off the machine and shut off the water supply before opening any fittings or removing the flowmeter. The machine operates at mains water pressure — water will spray if fittings are opened while the supply is on.
What the Flowmeter Cap Looks Like
The photos below show a GICAR flowmeter cap removed from a La Marzocco machine, with the O-ring and circlip laid out beside it. Note the discolouration and wear on the cap face — this is a typical failed unit.
What You'll Need
- Replacement flowmeter cap (see product below)
- Replacement O-ring (included or available separately)
- Circlip pliers or small flathead screwdriver
- Adjustable spanner
- Towel to catch residual water
Step-by-Step: How to Replace the Flowmeter Cap
Step 1 — Turn Off the Water Supply and the Machine
Shut off the water supply to the machine at the mains or the inline tap behind the machine. Switch the machine off at the main power switch. Do not just put it in standby — fully power it off. This ensures no water pressure remains in the system when you open the flowmeter.
Step 2 — Open the Expansion Valve to Release Pressure
Open the expansion valve (or steam wand) briefly to release any residual water pressure from the system. You'll hear a short hiss as the pressure drops. Once the hissing stops, the system is depressurised and safe to work on.
💡 Tip: Place a towel under the flowmeter before opening it — there will be residual water in the lines that will drip when the cap is removed.
Step 3 — Access the Flowmeter
Remove the side or top panel as required to access the flowmeter. On most La Marzocco machines the flowmeter is located on the inlet water line, typically near the pump. The GICAR flowmeter is a small square-bodied unit with a cap secured by a circlip.
Step 4 — Remove the Circlip and Old Cap
Using circlip pliers or a small flathead screwdriver, carefully remove the circlip that retains the flowmeter cap. Set the circlip aside — you will reuse it unless a new one is supplied with the replacement cap. Pull the old cap straight out of the flowmeter body. The O-ring will come out with it or remain in the body — remove and discard it.
Step 5 — Fit the New Cap and O-Ring
Fit the new O-ring into the groove on the new flowmeter cap or into the flowmeter body seat. Insert the new cap firmly into the flowmeter body — it should seat flush. Refit the circlip to lock the cap in place. Confirm the circlip is fully seated in its groove before proceeding.
Step 6 — Reassemble and Test
- Refit any panels removed during access
- Turn the water supply back on
- Power the machine on and allow it to heat to operating temperature
- Run a test shot and confirm the machine stops at the correct programmed volume
- Check around the flowmeter for any water leaks
💡 Tip: After replacing the flowmeter cap, you may need to reprogram your shot volumes as the new cap may read slightly differently to the old one. Run a few test shots and adjust the volumetric programming as needed.
🛒 Shop Flowmeter Parts
Frequently Asked Questions
How do I confirm the flowmeter cap is the fault and not the control board?
If the machine runs non-stop on all buttons (single, double, hot water), the flowmeter is the most likely cause — the board is not receiving pulse signals. If only one button is affected, the issue may be in the programming rather than the hardware. If replacing the flowmeter cap doesn't fix the fault, the flowmeter body or control board may need further diagnosis. Contact us for help.
Do I need to replace the O-ring at the same time?
Yes — always replace the O-ring when replacing the flowmeter cap. A worn O-ring will cause a water leak around the cap even if the new cap itself is fine. The O-ring is inexpensive and should be treated as a consumable whenever the cap is removed.
Does this apply to all La Marzocco models?
The GICAR flowmeter is used across a range of La Marzocco commercial and prosumer machines including the Linea Classic, Linea PB, GB5, and others. The cap and O-ring replacement process is the same across models. Contact us to confirm the correct part for your specific machine.
After replacing the cap, my shot volumes are still off — what next?
Reprogram your shot volumes after replacing the cap — the new cap may read slightly differently. If volumes are still inconsistent after reprogramming, the flowmeter body itself may be damaged or the impeller may be worn. Contact us for further diagnosis.
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