Meiko Commercial Dishwasher Error Codes 421-423: Holding Tank Low
Messages 421, 422 and 423 on a Meiko M-iClean U with reverse osmosis mean the holding tank water is insufficient, the maximum level was not reached, or the water feed is insufficient. Open the water inlet valve and check the pre-filter and sieve. If any of the three keeps showing, call us.
Medium: the final rinse water runs short, which slows or limits the work.
- Code
- 421 / 422 / 423
- Maker
- MEIKO
- Equipment
- Dish machines
- Applies to
- M-iClean U (red/gray messages)
What does MEIKO error code 421 / 422 / 423 mean?
The reverse osmosis system stores treated water in a holding tank so the machine has enough for each final rinse. The control watches the tank and reports three related states: 421, 422 and 423. The manual describes them as insufficient holding tank water, the maximum level not reached, and insufficient water feed. In each case the treated water the machine uses for the last rinse is running short. This can happen when the supply is restricted, when the membrane produces less than before, or when the tank sensing is not reading properly. Heavy back-to-back washing can also draw the tank down faster than the system refills it. The maker's steps are to open the water inlet valve and call a technician if the message does not clear. The first thing to do is give the system time to refill before the next load. If the three numbers recur after a pause, the supply, pre-filter and membrane are checked, followed by the tank level sensing and feed.
Affected models and control systems
This applies to Meiko M-iClean U undercounter dishwashers with a reverse osmosis system. It does not apply to machines without reverse osmosis, and other ranges use different messages.
Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.
What you may notice
- Message 421, 422 or 423 on the display
- Rinse that ends early or runs weak
- A longer wait between loads for the tank to refill
Possible causes
Listed in MEIKO's documentation
- Water inlet valve
- Pre-filter and sieve
- Reverse osmosis membrane and module
- Holding tank level sensing and feed
Other likely causes — what usually sits behind error code 421 / 422 / 423 on this control. A technician confirms which one it is before any part is replaced.
- Peak-hour washing that empties the tank faster than it refills
- A membrane that has slowed with age, so the tank takes much longer to fill
- Level sensing in the tank that is fouled and under-reads
Safe checks before calling for service
- Open the water inlet valve fully, as the maker says.
- Check the pre-filter and sieve for clogging.
- Give the system time to refill the holding tank before the next load.
- Note which of the three numbers shows and how soon after a heavy wash.
- If any of 421, 422 or 423 keeps showing, call us.
How a technician diagnoses error code 421 / 422 / 423
- Read which message is active and how often it returns.
- Check the inlet valve, strainer and pre-filter.
- Measure refill time of the tank from empty.
- Test the module output and inlet pressure.
- Check the tank level sensing and feed valve operation.
- Replace the membrane or sensor only after the tests.
- The tank, feed valve and module are pressurized water parts sitting close to live wiring.
- Measuring refill rate and module output needs timed tests with gauges.
- Tank level sensing reports to the control, and checking it means working inside the cabinet.
How error code 421 / 422 / 423 differs from similar codes
Message 410 reports the module supply, while 421 to 423 describe the holding tank level.
Technical reference
- Document
- M-iClean U Original operating instructions 9763258 (update 2026-06), 9.4.1 Messages p.43-45
- Edition
- 9763258 / Valid from: 2018-09 / Update: 2026-06
- Models / control
- M-iClean U (red/gray messages)
- Section
- 9.4.1 Messages, printed pp. 43-45 of 70 (PDF pp. 43-45)
- Checked
- October 2026
We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.
Related MEIKO dish machine error codes
What is the difference between 421, 422 and 423?
The manual groups them: tank water insufficient, maximum level not reached, and water feed insufficient. The fix path is the same.
Can I keep washing?
Wait for the tank to refill between loads, or the rinse will run short.
Will it clear itself?
It may after a rest if the supply is good. If it repeats, call us.
Need help with MEIKO error code 421 / 422 / 423?
A technician confirms the cause on site and gives you the price in writing before any work starts.