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Viessmann Vitodens 200-W B2HA - Heating not turning back on after DHW

HydronicRookie Member Posts: 54
edited October 2018 in THE MAIN WALL
Hi all, I thought I'd try on here to see if anyone has experienced the heating not turning back on after the scheduled priority DHW call is done. This behaviour may not continue into the future, but the current fix is to put the boiler on standby and then switch it back to DHW & Heating. Our boiler is the Viessmann Vitodens 200-W B2HA and it's working solely off of outdoor reset. Our outdoor temp has been around 9˚C the last couple of days with the indoor setpoint of 19˚C.

We're noticing this now as we turn the heat back on for the Fall, but we had issues last year where once in a while the reduced temperature wouldn't hold (i.e. the boiler wouldn't heat) during the reduced period - we ended up doing away with the reduced schedule all together.

Also of note (and this may be unrelated / a topic for another thread), but we've had a Flow-Rate Sensor error
code 1D for some time now that we've mostly ignored.

Thanks in advance,


  • Paul Pollets
    Paul Pollets Member Posts: 3,658
    Have you spoken with Viessmann tech services? You may have a faulty computer board.
  • HydronicRookie
    HydronicRookie Member Posts: 54
    Hey Paul, thanks for the reply and sry for the delay in following up -- the notification of your reply got buried in my inbox.

    I spoke with Viessmann today and upon digging into coding level two, we found the reason the boiler wasn't firing was related to the flow-rate sensor. It seems the the fault code 1D `Flow-Rate Sensor` although not blocking all the the time eventually causes the boiler not to fire up.

    We started seeing this fault right after commissioning the boiler, so today I went ahead and removed the flow-rate switch to flush out any debris that might have lodged itself after the initial and subsequent fills. After putting it back, the fault remains, so I'm thinking about just getting a new one in case it was faulty from the beginning.

    Perhaps there is some other flow-rate related part that I'm not thinking of.

    It seems amazing that the switch would be faulty, but then again, I also rendered a coding card useless after removing and re-inserting a couple of times and had to replace it.