Viessmann system boiler 100W or 200W

[Mr.B]

I am a home user and not a pro and would like to clarify as a user that I did check with Viessmann UK and they confirmed and it is written in MI as well that OV boiler can be used in a pressurised or seal system too.

Thank you. To be honest I'd taken it for granted and, additionally, the installer did too.

I realise pressurizing it has advantages and is the better option .... I just wish there wasn't the possibility of the extra pressure popping a joint, or even just causing a slight weep. Because the first floor is fully carpeted and has 8x4 chipboard flooring it would be a nightmare to have to start ripping it up to find the leak.

 

[Mr.B]

Thanks again for the helpful points and observations above in response to my question(s).

Lots of points were raised in the replies ..... for example rubber flow and return hoses to and from earlier Viessman heat exchangers which clogged and/or rotted but which now seem to have been replaced by copper.

Another point raised was about assessing the correct heat output of the boiler and heat loss calculations. I did my own calcs using a Mears but did see several comments online that suggested a Mears over estimated the required output of the rads - but I took one online calculator chosen at random and compared their finding (having input the required information), and it turned out that my front room (for example) required 5500 btu/h using the Mears ... but required something like 5650 using the online calculator - so not a million miles apart but the Mears didn't over estimate at all in that particular circumstance.

Another topic for considerion ..... whether a sealed system with a Viessmann boiler should have inhibitor in the system Viessman specifically say they do not recommend inhibitor in a sealed system but might tolerate it in an open vent system. That's an interesting one. The installer that called yesterday said that in Germany they usually fit a complete (sealed) system - pipework, boiler etc, rather than just swap this or that part that we might do over here and then fill it with purified water and NO inhibitor. He favoured putting a cleaning chemical in and leaving it for a few days, then flushing and refilling WITH an inhibitor in place and I believe he mean't that to apply to both open vent and sealed.

He also estimated (a rather impressive mental calculation in his head) that my open vent system will be pressurised (by virtue of the weight of water from the header tank to the ....etc etc....you all know the drill ....) to approx half a bar. I worked it out myself on a calculator using the conversions relevant to the exercise and made him spot on. Viessmann say the installer should pressurize a sealed system to 0.8 bar (and, of course, it'll increase when heated ... maybe by half a bar???) ... so maybe I'm worrying unduly about the possible leaks that could occur if/when pressurized with an expansion vessel - as opposed to leaving it open vent. At the moment I'm leaning towards insisting on a Stainless HEX and pressurizing it. And as the only two makes of boiler (that I can see) that do a stainless HEX are Viessmann and Alpha that rather limits the choice.

But, further acknowledgement of the time taken by other in trying to help.

 

[JohnD]

He also estimated (a rather impressive mental calculation in his head) that my open vent system will be pressurised (by virtue of the weight of water from the header tank to the ....etc etc....you all know the drill ....) to approx half a bar.

Extremely easy calculation, actually. I have quite a tall house and the cold water tank is almost exactly ten metres above the ground floor sink and shower

Ten metres of water height gives 1bar of pressure*

Is yours five metres?

It is harder for Americans who work in feet and p.s.i.
100 feet is approximately 43.3 psi.

*0.981 is near enough

 

[Mr.B]

Please bear in mind that maths wasn't my strong point at school (which I left in 1967 having gained remarkably little in the way of qualifications) and has gone downhill ever since.

In feet ......

Ground floor ceiling height 7.5
1st floor ceiling height 7.5
Joist between ground floor and 1st floor 1.0
Header tank raised in loft 2.0

Equals 18 feet

18 feet multiplied by 0.433 equals 7.79 psi

7.79 psi converted to bar equals 0.53 bar

Completed with the help of Google for the conversion figures.

 

[Notch7]

Please bear in mind that maths wasn't my strong point at school (which I left in 1967 having gained remarkably little in the way of qualifications) and has gone downhill ever since.

In feet ......

Ground floor ceiling height 7.5
1st floor ceiling height 7.5
Joist between ground floor and 1st floor 1.0
Header tank raised in loft 2.0

Equals 18 feet

18 feet multiplied by 0.433 equals 7.79 psi

7.79 psi converted to bar equals 0.53 bar

Completed with the help of Google for the conversion figures.

or more simply: 1 bar = 10 metres

I was born in 1965 but years of working in joinery manufacture has made me think in metres and millimetres not feet and inches

 

[Mr.B]

It would appear that 18 feet is just shy of five and a half metres.

I have to say at the age of 73 I work in a mix of metric and imperial, often using both in the same sentence. And will do until I'm no longer here I'm sure.

 

[JohnD]

It would appear that 18 feet is just shy of five and a half metres.

Five and a half bar then, or just under.

No calculation needed, really, and no Google.

Edit
You are right, 0.55

 

[MNW67]

Five and a half bar then, or just under.

0.55 bar? I get confused by this all the time, but I think this is right!

 

[Mr.B]

I'm confident we agree.
Equally important I'm a bit more reassured now I know that pressurising the system to 0.8 bar (plus the extra pressure when it heats up) isn't quite as risky as I had feared up to now. It's been my main fear given those pesky 8x4 sheets of chipboard nailed in place and the presence of a 28 year old 10mm soldered microbore system hidden underneath them, and secreted behind dot and dab plasterboard, as all the downstairs drops are.