Viessmann F2 fault code and pump overrun

Discussion in 'Plumbers' Talk' started by fronty, Dec 15, 2018.

  1. fronty

    fronty New Member

    My new Viessmann didn't start up tonight when the roomstat called for heat. I noticed it was reporting an F2 fault, which seems to be something to do with a temperature limit. I did a reset and it fired, then I wondered what might have caused it.

    After a while the roomstat eventually shut down the boiler and I checked if the pump was overrunning (it used to overrun for about 5 mins on my old boiler). There was no sign of life up there, the pump was completely shut down. Then I watched the temperature on the boiler rise over the next 15 mins from around 65 degrees to 92, before it started to drop. Obviously the latent temperature of the water in the heat exchanger.

    I was running the boiler about 10 degrees hotter earlier, so temp was around 76 degrees, so was thinking maybe when it shut down the temp reached somewhere around 100-105 degrees - maybe that's why the F2 fault was reported, I don't know what temp it occurs at. Anyone know?

    Doing some googling I read that on the Vitodens 100w pump overrun is not required, but I'm concerned that if if the rise in latent temp was the cause of the F2 fault, it's going to cause me aggro with the wife if the heating doesn't come on in the morning.

    How easy is it to enable overrun? Is it a boiler setting somewere?
  2. The Teach

    The Teach Screwfix Select

    Thats true,the installer has to understand that before choosing a boiler without pump over run.

    Usually the vitodens has an internal wiring connection for the pump,an optional plug-in pcb connector is required & should have been supplied along with specific wiring instructions. Maybe ask the manufacture or installer about the pros & cons re the pump over run facility.

  3. Mike83

    Mike83 Screwfix Select

    Pump overruns cause no issues and should be standard on all boilers.
    It’s crazy not having them.

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