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Grundfos STP 2 fault 6B

Unstable water temperature or noisy pump (too high water temperature)

Shower pump

What it means

Water temperature too high causes unstable temperature or noisy pump.

Likely causes

  1. Too high water temperature
  2. Solder joint heat damaging plastic pump components
  3. Air pockets from incorrectly routed pipework
  4. Restricted or kinked flexible hoses
  5. Additional outlet fittings on inlet pipework causing incorrect flow switch operation

Where to start

  1. Check hot-water cylinder temperature setting
  2. Verify hot water cylinder supply feeds a pump with its own dedicated supply
  3. Confirm surrey flange fitted to minimize air ingress from hot water source

The full answer, free

  • 10 more checks in order
  • The readings and component tests from the manual
  • How to put it right, step by step
  • The manual page for this fault (page 14), right under the answer
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Safety: Isolate power and water, and prove dead before you open or test the pump.

From the Grundfos manual for the STP 2. Check the model on the data plate before you order parts.

Other Grundfos STP 2 fault codes