The mechanical seal to suit the Grundfos JP5 is a replacement shaft seal for a 12 mm shaft. It fits the JP5 and units labelled JP5-B, and the same seal is used in the Grundfos JP6. Measure the shaft where your old seal sat, or compare the old seal with the photos, before fitting it.
Which pumps use the same seal as the Grundfos JP5
This 12 mm seal is shared with the Grundfos JP6. It is also matched to several pumps we do not have model pages for: the Grundfos SPK, Lowara BG, Lowara SG, early Lowara C Series and Saer FC20. The same seal is sold on its own as our 12 mm mechanical seal.
A shared-seal list is a guide, not a guarantee: pump makers can change parts during a model’s life, and an older pump may have been repaired with a different seal. The shaft diameter and the shape of the old seal are what confirm the fit.
Signs the JP5 seal has failed
A mechanical seal works by two flat faces running against each other, one turning with the shaft and one fixed in the housing. Grit, running dry or plain age wears those faces until water gets past. Left alone, the leak usually gets worse rather than better.
- Water dripping from the gap between the pump housing and the motor.
- The pressure switch cycling the pump on and off with every tap closed.
- A damp patch, white scale or rust streaks under the motor.
Fitting notes for the 12 mm seal
The steps below are the usual sequence for a jet pump seal change; follow any instructions that came with your pump where they differ. Turn off and isolate the power, close the valves and drain the pump before you start. Separate the motor from the pump housing, remove the impeller and slide the old rotating half off the shaft, then push out the old stationary seat. Clean the seat recess and the shaft so both are smooth.
Keep the new seal faces clean and do not touch them with your fingers. Lubricate the rubber parts with a little water or soapy water rather than grease, press the seat in square, and refit the impeller. Prime the pump fully before switching it on, because even a short dry run can damage new faces.
If the JP5 has also been slow to start, the Grundfos JP5 service kit pairs this seal with the run capacitor for one job. Seals and kits for other models are on our Grundfos service kits page, and unused parts can go back under our returns policy.
Before you order
Check the old part before fitting: match the size of your old seal.
Capacitor details for this pump: Grundfos JP5 capacitor guide.