Nov 1997: TB3154 - Condensate Pump Maintenance

24th November 1997


  1. It is essential that the condensate pump system is regularly checked for correct operation. The frequency will depend on the environment in which the unit is operating but should be a minimum of once every 3 months. It is imperative that the system is checked following a long absence from cooling (e.g. winter in the UK).
  2. The sensor probes will be prone to contamination from dirt and dust particles. These will build up an insulating layer on the probes continually raising the operating level of the pump and overflow alarm. This, in turn, could stop the pump from activating and eventually cause an overflow from the sump. 
  3. The filter is provided to trap debris before it enters the inlet pipe to the pump. There will be an increasing accumulation on the mesh which could lead to blockage, especially if the sump is allowed to dry out (no cooling requirement) and then subjected to condensate. Any blockages of the filter will result in a reduced, or no, condensate flow and eventually cause an overflow from the sump and noise from the pump. 
  4. Any trapped or kinked hoses will reduce, if not stop, flow leading to noise and overflow problems.



  1. If possible, manually drain the condensate sump (most products have drain down hose).
  2. Refer to the unit installation instruction to gain access to the condensate sump, condensate pump and filter assembly. 
  3. Condensate sump: Using a cloth and warm, soapy water, remove any debris which has accumulated in the sump. Thoroughly dry the sump. 
  4. Filter assembly (if fitted): Remove the filter assembly from the sensor assembly; flush through with warm soapy water and rinse with clean water. 
  5. Sensor Assembly: Remove the sensor assembly and clean in warm, soapy water. Any difficult contaminations may be removed by scrubbing with a small, soft brush and a mild detergent. Ensure that the pump suction is not kinked. 
  6. Discharge hose: Ensure the pump discharge hose is not kinked and the connection to a drain hose is secure. 
  7. Further checks: Ensure that all electrical connections are secure and all pipes are fully pushed on to inlet and outlet drain connectors.  Ensure that the filter and sensor assembly are refitted correctly and are secure. 
  8. System commissioning: Reconnect the supply to the unit. Allow approximately one minute for the controls and sensor to stabalize. Slowly add water to the condensate tray sump until the pump runs. Initially the pump will be noisy until the air in the bottom hose has been expelled. It is possible that, on this first cycle, the pump will run dry for a short period (indicated by noise). Add more water to the sump and the pump will cycle in the normal manner. With the system in cooling mode, continue adding water to the sump until it reaches the higher of the sensor probes. The cooling cycle will shut down (on 'E' products an alarm will sound) and the pump will continue to run until the water has dropped below the level of this probe.

NOTE:  Whenever the electrical supply to a unit fitted with a condensate pump and controls has been interrupted, a delay of up to 1 minute will occur before the compressor or the pump will start when the supply is reinstated.


  • Unit will not cool - No mains supply to the control board.
  • Pump does not run - Fuse on control board blown (315mA x 20mm). Sensor disconnected from control board. 
  • Cooling is interrupted - Restriction in pump flow allowing level to rise and trip overflow circuit. Check for blockage or kink in hoses.  Filter blocked - remove and clean. 
  • Excessive pump noise - Air leak in hoses and/or joints. Pumping without water in sump - control board fault; short circuit to chassis component. Loose connection between sensor and control board. Loose fuse, intermittent mains supply to control board. Water syphoning due to lack of air break. Filter blocked - remove and clean.


  1. The pump will work against a 5m head. Flow rate is highest with minimum head.
  2. Long lengths of drain pipe should not be exposed to the outdoor ambient, otherwise freezing of condensate may occur during winter operation. 
  3. Where the drain hose outlet is below the level of the pump, it is advisable to fit an air break to avoid syphoning. 
  4. Ensuring that no hose is kinked, as this could seriously affect the pump performance. 
  5. Clean the filter at regular intervals.