Grundfos STP 2 fault 5A

What it means

The use of other taps in the house may cause the pump to start momentarily, resulting in pulsing.

Likely causes

1. The use of other taps in the house may cause the pump to start momentarily
2. Water hammer
3. Low flow rates from cistern filling causing frequent pump cycling
4. Hot-water supply taken directly from top of hot-water cylinder
5. Entrapped air causing airlocks in supply pipe
6. Air not thoroughly purged from system
7. Leak in system
8. Drip in system
9. Air trapped in pump
10. Non-return valve incorrectly fitted in inlet pipe
11. Undersized tank causing insufficient supply
12. Incorrect outlet height causing hot-water-only delivery
13. Outlet positioned below mains inlet causing air ingress
14. Non-return valve fitted incorrectly in inlet pipe causing restricted flow or pump damage
15. Undersized pipework
16. Pipes routed under floor causing air traps
17. Other outlets fitted in inlet pipes
18. Shared (non-dedicated) hot/cold supplies
19. Blanked-off pipes
20. Restrictions in flexible hoses
21. Unsecured pipework
22. Direct mains connection causing pressure issues or pump damage
23. Jointing compounds/tape causing blockage or leaks
24. Shared supply pipe causing air ingress or reduced flow
25. Missing surrey flange causing air in hot water supply
26. Blocked strainers common on initial pump installation or new buildings due to jointing compounds, tapes, flux and debris flushed through system
27. Leak causing loss of tank air pressure
28. Leaks due to insufficient hose insertion depth
29. Debris ingress into pump causing blockage or damage if strainer omitted
30. Leaks due to under-tightened or incorrectly connected hoses
31. Mechanical strain on pump from misaligned pipework
32. Solder joint heat damaging plastic pump components
33. Air pockets from incorrectly routed pipework
34. Restricted or kinked flexible hoses
35. Additional outlet fittings on inlet pipework causing incorrect flow switch operation
36. Mechanical stress on pump from rigid pipe connection
37. Leaks from use of jointing compound instead of correct hose connections

Where to start

1. Check taps or other outlets for water hammer
2. Switch off power supply for ten seconds
3. Switch power supply back on