Grundfos STP 2 fault 4D

What it means

Continuous pump running due to a faulty or incorrectly set flow switch or reed switch.

Likely causes

1. Flow switch or reed switch faulty or incorrectly set
2. Entrapped air causing airlocks in supply pipe
3. Air not thoroughly purged from system
4. Air trapped in pump
5. Blocked strainers common on initial pump installation or new buildings due to jointing compounds, tapes, flux and debris flushed through system
6. Leak causing loss of tank air pressure
7. Low flow rates from cistern filling causing frequent pump cycling
8. Pipes routed under floor causing air traps
9. Solder joint heat damaging plastic pump components
10. Air pockets from incorrectly routed pipework
11. Additional outlet fittings on inlet pipework causing incorrect flow switch operation
12. Debris ingress into pump causing blockage or damage if strainer omitted

Where to start

1. Test flow switch/reed switch operation
2. Inspect for airlocks in supply pipe
3. Purge all air from system