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Thread: Pump overrun

  1. #21
    Automated Home Legend
    Join Date
    May 2014


    Thanks - that's interesting. I was told that without the HW Demand box, the HW would just heat at the modulated boiler output temperature.

  2. #22
    Automated Home Jr Member
    Join Date
    Nov 2016


    Quote Originally Posted by HenGus View Post
    Sorry to thread creep. I m looking at the Viessmann with O/T. How is the HW BDR configured to get 80c HW? I was told that the HW demand box is a must. Out-of-interest, what size of boiler do you have? I ask because I have a 5 bed modern property (15 years old) with an Ideal FF280 (24kW). One installer has suggested that I need a 32kW, and another a 24kW but I could go as low as 18kW!!

    As a fellow viessman owner, I have a 26kw version, 3 floors 14 rads in the 60 year old house. I also thought I needed the demand box so bought it, but then tried it without connecting it up and the opentherm upped the temp to 78c when hw demand. Can sell you my box if you need one!

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