Meiko UPster U 400 M2 Error Code ERR 304: Tank Temperature Not Reached
ERR 304 on a Meiko UPster U 400 M2 means the tank temperature was not reached after the maximum heat time set in parameter P314. The maker says it is not possible to continue and to call a technician. Switch the machine off, let it cool, and check that the water supply is open.
High: the machine stops and will not run until the heating is repaired.
- Code
- ERR 304
- Maker
- MEIKO
- Equipment
- Dish machines
- Applies to
- UPster U 400 M2
What does MEIKO error code ERR 304 mean?
Before it washes, the UPster U 400 M2 heats the tank water to the working temperature. The control gives the heating a maximum time to do this, held in parameter P314. If the temperature has not been reached when that time runs out, the control stops and shows ERR 304. It does this because a wash at the wrong temperature will not clean or sanitize properly, and because a heating circuit that cannot reach temperature may have a real problem. The manual lists the likely places to look: the tank heating element and its relay, the tank temperature sensor, whether the tank is filled to the right level, and scale on the heating parts. A tank that is low on water, for example, can mislead the heating, while a scaled element transfers heat poorly and takes far too long. A weak or failed element, a relay that does not close, or a sensor that reads low all lead to the same message. The maker says it is not possible to continue, so staff cannot work around it. The operator's part is to make sure the water supply is open and the tank is filling.
Affected models and control systems
This applies to the Meiko UPster U 400 M2 glass and dishwasher. Other Meiko models and other controller generations use different numbers for heating errors.
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
- ERR 304 on the display
- Tank water that stays lukewarm
- Machine that stops during warm-up
- Long wait at the start of the day with no heat
Possible causes
Listed in MEIKO's documentation
- Tank heating element and its relay
- Tank temperature sensor
- Tank filled to the right level
- Scale on the heating parts
Other likely causes — what usually sits behind error code ERR 304 on this control. A technician confirms which one it is before any part is replaced.
- Element partly failed, so it heats but far too slowly
- Heavy limescale insulating the element from the water
- Heating relay contacts burned so only part of the power reaches the element
Safe checks before calling for service
- Switch the machine off and let it cool.
- Check that the water supply is open and the tank is filling.
- Do not try to continue. The maker says it is not possible.
- Note whether the water felt cold, warm or hot.
- Call us. We test the element, the relay and the sensor.
How a technician diagnoses error code ERR 304
- Read ERR 304 and check the P314 heat time setting.
- Confirm tank level and fill.
- Measure element resistance and supply voltage under load.
- Test the heating relay or contactor with a meter.
- Compare the tank sensor reading with a probe thermometer.
- Descale or replace the failed part only after the tests.
- The tank element and its relay run on live 208-240 V wiring with high current.
- Checking the heat time parameter means working in the machine's service settings.
- A sensor reading wrong looks like a weak element, and only a meter and probe separate them.
How error code ERR 304 differs from similar codes
ERR 310 to 312 point to the tank temperature sensor circuit, while ERR 304 is the heat-up taking too long.
Technical reference
- Document
- UPster U 400 M2 Original operating instructions 9760441 (update 2026-06), 9.6.1 Messages p.33-35
- Edition
- 9760441 / Valid from: 2018-02 / Update: 2026-06
- Models / control
- UPster U 400 M2
- Section
- 9.6.1 Messages: INFO table printed p. 33, ERR table pp. 34-35 (of 50)
- 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
Can I wash with cool water for a while?
No. The maker says it is not possible to continue, and cool water will not clean or sanitize properly.
Will ERR 304 clear itself?
Only if the cause was a closed valve or low water. A restart will tell you.
Is descaling the fix?
Sometimes, if scale is the cause. A technician checks the element before deciding.
Need help with MEIKO error code ERR 304?
A technician confirms the cause on site and gives you the price in writing before any work starts.