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Ideal Logic System IE fault F0U

Flow/return differential greater than 50°C

Gas boiler

What it means

Boiler has detected a flow/return temperature differential exceeding 50°C.

Likely causes

  1. Flow/Return differential fault as referenced in Section 4.14
  2. Isolation valves closed
  3. Pump not operating
  4. Radiator valves closed
  5. System blockages
  6. Pump not operating (wiring fault or pump failure)
  7. System blockage restricting flow

Where to start

  1. Refer to Section 4.14: Flow/Return Differential greater than 50°C
  2. Check if isolation valves are open
  3. Check if pump is operating

The full answer, free

  • 3 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 49), right under the answer
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Safety: Isolate gas and power before you open the case. If you have been into the gas side, do a tightness test, and a combustion and flue check before you hand back. Gas Safe (UK) or RGI (Ireland) work only.

From the Ideal manual for the Logic System IE. Check the model on the data plate before you order parts.

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