Troubleshooting 'piston blocked error' on dosino/dosing unit. 

How do you know you have this problem?

The piston blocked error occurs due to some sort of resistance applied to the piston when in motion. It is not often caused by the dosino itself. 

What can I try to resolve it?

1. The tubing, buret tip and/or antidiffusion valve are often the culprits. 
2. Inspect the tubing from the dosing unit to the titration vessel for blockages. 
3. Inspect the antidiffusion valve (replace if necessary, part number 6.2726.090):

1. Disassemble and clean the dosing unit per the following video: Titration - How to clean the dosing unit

What are some ways to prevent the problem?

1. Metrohm recommends replacing the glass cylinder annually. 
2. Dosing units require regular inspections and must be disassembled down to the cylinder unit from time to time and cleaned as necessary. 
3. Monthly or even weekly inspections are called for in the event that alkali, corrosive or high concentration reagents are used. If non-problematic reagents are used, then the inspection intervals can be extended to between six and twelve months. 
4. If aggressive reagents are dosed with dosing units, then such units should be rinsed with an inert solvent when not in use ('PREP'/Prepare function) and then subsequently emptied ('EMPTY'/Empty function). 
5. In the event that the dosing unit is not in use for > 2 days, the dosing unit should be emptied without fail, because even water can corrode the buret glass in the event of prolonged periods of disuse. Remove the dosing drive (dosino) in the event of prolonged periods of disuse (longer than one week). 

Additional Support

If you encounter any issues or need additional help, please submit a support ticket through Metrohm Technical Support. 

For additional training on any of these topics, explore our available Metrohm Titration Training courses or learn more about our Metrohm Custom Training options.