Viessmann min gas working pressure

[eagleeye]

Can anybody tell me what the minimum gas working pressure is on the Viessmann 100-W 35kW combi. Going by what it says in the MI's it can be between 10-34mb. Or am I reading this wrong ? See attached from MI's.

 

[ShaunCorbs]

I’m guessing that’s a us instructions may I ask why your asking ?

 

[eagleeye]

Think it is Shaun as it's in w.c rather than mb. One of or installers has asked me as he couldn't find it in the MI's. He said he has 17mb at gas valve but I've spoken to Viessmann before about this and they told me a loss of 2.5mb may be across valve. I still think it's too low anyway as he didn't test it with the gas cooker on and had 21mb working at the meter

I’m guessing that’s a us instructions may I ask why your asking ?

 

[ShaunCorbs]

Think it is Shaun as it's in w.c rather than mb. One of or installers has asked me as he couldn't find it in the MI's. He said he has 17mb at gas valve but I've spoken to Viessmann before about this and they told me a loss of 2.5mb may be across valve. I still think it's too low anyway as he didn't test it with the gas cooker on and had 21mb working at the meter

sounds on the low side there ok down to around 14 but that’s with the meter wp at 16.5

I would say pipe sizing is an issue to something’s blocked a bit

 

[eagleeye]

sounds on the low side there ok down to around 14 but that’s with the meter wp at 16.5

I would say pipe sizing is an issue to something’s blocked a bit

Yeah definitely not right. I'd always do a 35kw on 28mm tbh. It's only on 22 off meter and 10mtr run. Upgrade time !! Last time I spoke to viessmann they did actually advise that we fit a test point before it goes into boiler so a true reading can be obtained.

 

[snowhead]

 

[townfanjon]

It depends on the age of the boiler, it used to be 17.5 mbar
The table above from Snowhead is the new one , depending on the boiler .

 

[ShaunCorbs]

Yeah definitely not right. I'd always do a 35kw on 28mm tbh. It's only on 22 off meter and 10mtr run. Upgrade time !! Last time I spoke to viessmann they did actually advise that we fit a test point before it goes into boiler so a true reading can be obtained.

most manufacturers recommend this these days but I don’t understand why something can’t be built into the gas iso valve

 

[eagleeye]

View attachment 45623

Thanks mate. Crazy to think it would work down to 10mb isnt it. Problem is though it's more than 1mb between meter and boiler. But that said, if its currently 21 at boiler and 17 at meter, should the pressure at meter ever drop to 14 then the boiler would still be ok !!
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most manufacturers recommend this these days but I don’t understand why something can’t be built into the gas iso valve

Yeah it madness isnt it. I know the Vaillant EcoTec have them but no others do. As you say it should be made standard