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Ecodan Immersion heating water after 15 minutes of pump heating

  • March 16, 2026
  • 3 replies
  • 19 views
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Rank 1

Hi, 

New to the forum. I have an Ecodan for the last 3 years without much problem. Heats 2 zones and DHW. A few weeks ago I had a low flow error that i got a technician to fix, He cleaned the pipes out and it’s back to good flow, but since then i have noticed that when the water is heating, the heat pump comes on for about 15-20 mins, then it switches to immersion for 15-20 minutes and back and forth until the water is back to 50 Degrees. See graph below. I’m wondering is there a setting in the FTC5 that he might have switched while troubleshooting and forgot to reset. 

Thanks in advance for any help/thoughts

 

3 replies

BPLightlog
Super User
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  • BPLightlogSuper User
  • Super User
  • March 16, 2026

Hi ​@Pluto , if you’ve checked the set point and reheat settings, it might be something that’s moved on the hot water cylinder sensor which falsely indicates that it’s up to temp.

Do you know your flow rate? Just wondering if the rate might be near minimum still.

Bring me Sunshine ~ E&E {Solar PV, Battery Storage, Hybrid EV, ASHP and Home Assistant automation}
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  • Pluto
  • Author
  • Rank 1
  • March 16, 2026

Set point is 51, temp drop 10 Degrees and i just checked flowrate as the water was heating - it was 13L

    BPLightlog
    Super User
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    • BPLightlogSuper User
    • Super User
    • March 16, 2026

    13l/min should be good enough.

    What about the cylinder sensor? If it got moved slightly, it might give false ‘target achieved’ readings as the DHW is heating - at that point the system would switch back to alternative heating before the false ‘target achieved’ lowers before getting to real target. That would create the on/off effect.

    Another alternative might be if the 3 way diverter valve is not switching cleanly

    Bring me Sunshine ~ E&E {Solar PV, Battery Storage, Hybrid EV, ASHP and Home Assistant automation}
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