Troubleshooting
Contact our Technical Service Department at 1-800-888-3743 or by e-mail at techservice@finishthompson.com if you have any questions regarding product operation or repair.
Sealless Centrifugal Pump
General Notes:
- Do not pump liquids containing ferrous metal fines.

- If magnets decouple, stop pump immediately. Operating the pump with the magnets decoupled will eventually weaken the magnets.
- Do not use mismatched drive magnet assemblies (different number of magnets on inner and outer drive magnet assemblies).
No or Insufficient Discharge
- Air leaks in suction piping
- Pump not primed
- System head higher than anticipated
- Closed valve
- Viscosity or specific gravity too high
- Motor too large for magnet coupling rating (magnets uncoupled)
- Suction lift too high or insufficient NPSH
- Clogged suction line or impeller vanes
- Motor rotation incorrect (correct rotation when viewed from the fan end is clockwise - except DB3-5.5 models)
Insufficient Pressure
- Air or gas in liquid
- Impeller diameter too small
- System head lower than anticipated
- Motors speed insufficient (too low) or motor rotation incorrect (correct rotation when viewed from the fan end is clockwise - except DB3-5.5 models)
Loss of Prime
- Leak in suction piping
- Foot valve or suction opening not submerged enough
- Foot valve too small or leaking
- Air or gas in liquid
- Foreign matter in impeller
- Leaking valve. Suction lift too high or insufficient NPSHa.
Excessive Power Consumption
- Head lower than rating
- Excessive flow
- Specific gravity or viscosity too high.
Vibration/Noise
- Loose magnet
- Drive magnet rubbing
- Pump cavitating from improper suction or feed
- Motor or piping not properly secured
- Foreign object in impeller
Won’t Prime (SP Series Only)
- Did not fill housing with fluid before initially starting pump
- Closed discharge valve (valve should be open or open air vent line)
- Leak in suction piping
- Suction pipe not submerged enough (causing a vortex or exposing the end of the suction pipe)
- Lift exceeds pump ability (see SP11/15 Capabilities section)
- Suction pipe diameter too large
- Specific gravity or local atmospheric pressure (altitude/elevation) not accounted for in lift calculations
- Mismatch of inner volute and impeller diameter
- Inner volute o-ring chemically attacked, cut, brittle, etc.
- Motor rotation incorrect (correct rotation when viewed from the fan end is clockwise)
- Check valve installed too close to the pump
Primes Slowly (SP Series Only)
- Mismatch of inner volute and impeller diameter
- Suction pipe diameter too large (larger than 1 1/2”)
- Closed discharge valve (valve should be open)
- Inner volute o-ring chemically attacked, cut, brittle, etc.
Drum Pump
- Ensure adequate power/air pressure being supplied to motor
- For electric motors, if a manual circuit breaker is present, push to reset
- Ensure that the pump and motor model is assembled correctly using the required coupling insert as instructed per the manual
- Confirm there are no obstructions or restrictions in the discharge hose affecting the performance or flow rate
- Make sure the application fluid and application parameters fall within the capabilities of the pump/motor combination selected