Converting old vented central heating system to unvented

Micklee

Hi,

I am fitting a second hand pellet boiler at home, taking out a firebird popular.

New boiler throwing a code saying low water pressure, haven't enough head in the attic. Waiting to hear from manufacturerto see if I can adjust the low water pressure parameter, so this may not be needed, but I may need to convert the system to a pressurised system.

Question is, does the following make sense as a way of doing it? I'm not a plumber so bear with me on the lingo.

I'm also not converting the hot water tank to ventless, just the boiler circuits.

I was thinking of sticking a non return valve on the fill pipe from the header tank in the attic, and dead ending the vent pipe into an air bleeder and pressure vessel before it goes off into the attic (vent pipe tees off the coil in hot water cylinder) so the pressure vessel would end up in the hot press above HWC.

Thinking this way it can still auto fill if it needs to for some reason, or if that's a problem I can just use a ball valve instead of the non return valve.

Seems to me this is the least intrusive way of doing it? Interested to know if this is a standard method of doing it or not, I have no idea.

10-10-20

Hi, have a look at this thread:

https://www.boards.ie/discussion/comment/121832383#Comment_121832383

...and then this thread:

https://www.boards.ie/discussion/2058341799/sizing-an-expansion-vessel-help-needed

DublinDilbert

https://www.boards.ie/discussion/2058342129/converting-old-vented-central-heating-system-to-unvented

In general most boilers need 1 bar of pressure minimum, but the head from your small attic tank, assuming a 2 story house is probably about 0.4 bar. Make sure you have a 3 bar pressure relief valve fitted outside at the boiler. Then yes you can fit an expansion vessel / bleeder on the old vent pipe in the hot press and a filling loop on the pipe that is was coming from the small attic tank.

Make sure to get a filling loop with a pressure gauge on it, also remember if you are filling in a second story hot press that you only need to fill to 0.6 bar and you will have approx 1 bar the boiler.