ENO-20/30 NOx Analyzer shows Error 3

The ENO-20 gives error 3 when its pressure is unstable. There are two sensors on the pump, pressure sensor and rotating sensor of the pulley. If one of these gives an abnormal signal, the pump will generate error 3. 


Please confirm if pump gives an error when you run the pump opening the drain valve. The pump will not get any back pressure.  If the the pump gives error 3 when the valve is open, it is because of the malfunctioned sensor for pressure or rotation of the pump, or a program error on the pump. The pump may have accidentally loaded the incorrect program.  It is not complicated to delete. 


To clear the program issue, please try below. If you did not find an error when the valve was open, please skip this paragraph. If this did not work, it means there is a sensor problem and you need to contact us.

1. Open the drain valve of the Carrier Pump to avoid giving a pressure on the pump. (If the problem is on the Reactor, please work on the Reactor pump instead of the Carrier pump.)

2. Turn off the main power on the back panel once and power on. 

Press and hold these three buttons together; SET button of Carrier Pump, Check button and Autozero button. Keep these three key pressed and hit the Start/Stop key. Once the system starts, please release all keys. The display of the carrier pump should display 2. If so, please hit the Set Key three times and the pump should start to run. If not, please change the number with the arrow key and show "2" and hit the Set key three times and the system should start.  Let the system run for a few minutes and then confirm whether the pump has an error or not. 

3. If it is OK, please shut down the system, close the pump drain and run by pressing only Start/Stop.


If you do NOT find Error 3 when you open the valve, it indicates that the check valve is not working properly. This is usually because of the contamination of the check valve.  Please clean up check valves. The procedure is shown in the attached file. If you are not comfortable to clean the check valve by yourself, you can buy new check valves. To find which check valves have a problem, please try to remove one of them and replace to the corresponding check valve of the other pump, such as the reactor pump.

Derek is the author of this solution article.

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