Viessman low pressure, DHW back flush

pepinbilt

Hi there 
I have a Viessman vitodens 100-w as well as a combiplus DHW add on.
I know little to nothing about my system, it has been in my house for a handful of years.

I have noticed as of recent my boiler does not maintain system pressure the way I think it should. It has been hovering around 5 psi lately. I have looked on YouTube but my Viessman seems to be different as I can’t figure out how to introduce pressure back in.

Also, my DHW has never been back flushed and I was hoping I could get some help on how to do it properly. I assume vinegar is fine to flush? 

Is it just as simple as feeding into the supply from a 5 gal bucket and pump, and catching the return while having the house side isolated?
any info helps. Thanks a bunch.
.
.how to 

Derheatmeister

As for the Pressure....
Not a Viessmann Issue..
Your system has a automatic fill valve which looks like a bell with a lever on top, It is probaby in need of replacement?
BTW..It looks like the Back flow preventer and Fill valve installation was reversed and or installed backwards(In the wrong direction) !

As for the Flush..We use a flush kit which has a color changing agent for flushing the HX...This works much better that vinegar. Low energy Systems in Denver Colorado has these kits 1 800 873 3507

pepinbilt

I just found my boiler manual and it looks like the valve directly under the right side of the boiler is a fill.. which is the same spot I see all the rest of the vitodens 100 on YouTube with the fill you speak of.. but if I understand correctly I should just be able to hook this up to domestic cold and refill boiler back up to around 15-20 pounds or 1-1.5 bar?
things just aren’t performing like they used to and our upstairs heat goes “thud thud” every time it comes on, it’s enough to wake our kid up lol. Understand it’s part of the hydronic system but I also wonder if the low pressure is contributing to this as well 

neilc

you have an auto fill, pressure reducing valve,
to the right of the boiler, bottom edge,
right side of the tee the expansion tank is piped to,
lift that little lever on top and let it snap back down,
you should hear a water flow,
keep your eye on the boiler pressure,
if the auto fil sticks open, be ready the close a ball valve to it,

what is the boiler pressure ?
before and after,

actually, while the boiler is still down at 5 psi,
check the air pressure in the expansion tank,
it should be at at least 12, 15 psi,
a bicycle pump works

pepinbilt

With some instruction I had repressurized with this up to about 12# and is now holding there. Seems a heck of a lot quieter now it was sounding almost a lot like cavitation before 
thanks 

neilc

the green fixture under the expansion tank is an air separator,
the vent on top of it,
is that cap loose, so air can get out ?

pepinbilt

Looks to be all good there