Originally posted by victorp1612
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Pump overrun
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Originally posted by Norfolkboy View PostThanks for this once mine gets going it does s a good job, just seems a little strange getting up to desired temp. Did you need the optional hot water demand box from viessman, to get max flow temp when hw is called, I didn't but read another member that did have to- gets me thinking if their are different versions of the software in the boiler
Opentherm module attached to boiler and a BDR controlling the HW.
As a matter of interest, do you have dials ( knobs ) on your viessman or is everything controlled through the touch screen ? ( wondering if we have the exact same model - I have the touch screen model )
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Originally posted by victorp1612 View PostNo additional Viessman boxes , just the plain boiler and the evohome.
Opentherm module attached to boiler and a BDR controlling the HW.
As a matter of interest, do you have dials ( knobs ) on your viessman or is everything controlled through the touch screen ? ( wondering if we have the exact same model - I have the touch screen model )
I don't have a touchscreen, can you adjust the boiler setup on that? I am unable adjust anything on mine, which may help with the short cycling I'm seeing sometimes
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Originally posted by victorp1612 View PostYep , sorry I should have added that I'm using Opentherm with a Vitodens 100W. I have 9 Rads and the DHW kit on a S plan config - with a ABV installed.
I definitely see Opentherm modulating as when the heat demand is low , average temperature demand is 40 ( would need to check again ) with 1 bar on the burner output displayed on the boiler.
If the heat demand increases, so does burner output and water temp.
When DHW kicks in , it goes full blast - up to 80deg . Once the DHW time is over , it closes the valve on the cylinder and the boiler pump will then stop. It will however kick in again for a few seconds as the temperature rises. It usually does this 2 or 3 times over a 10 minute period until the boiler temp decreases.
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Originally posted by HenGus View PostSorry 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!!
For HW, I didn't do any special config. The sensor attached to the cylinder is connected to the BDR , which is then bound on the evohome as Stored Hotwater.
When HW comes on , the boiler fires up at 80 ( don't know why 80 ... I've checked the boiler config and see that HW temp can be set but it looks like the opentherm module over rides that setting )
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Originally posted by HenGus View PostSorry 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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