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. Hot-water supply taken directly from top of hot-water cylinder
4. Entrapped air causing airlocks in supply pipe
5. Air not thoroughly purged from system
6. Leak in system
7. Drip in system
8. Air trapped in pump
9. Non-return valve incorrectly fitted in inlet pipe
10. Blocked strainers common on initial pump installation or new buildings due to jointing compounds, tapes, flux and debris flushed through system
11. Leak causing loss of tank air pressure
12. Low flow rates from cistern filling causing frequent pump cycling
13. Undersized pipework
14. Pipes routed under floor causing air traps
15. Other outlets fitted in inlet pipes
16. Shared (non-dedicated) hot/cold supplies
17. Blanked-off pipes
18. Restrictions in flexible hoses
19. Unsecured pipework
20. Debris ingress into pump causing blockage or damage if strainer omitted

Where to start

1. Check taps or other outlets for water hammer
2. Check hot-water supply connection point on cylinder
3. Inspect for airlocks in supply pipe