low pressure after replacing radiator

[Dr_Doolittle]

I posted here a while ago asking how to top-up my system.
see here:
//www.diynot.com/forums/viewtopic.php?p=638940#638940

here's an updated schematic:

http://i187.photobucket.com/albums/x228/Dr_Doolittle/Pipescopy-1.jpg
note:
-valve B is left open, with the handle removed.
-non return valve after valve A
-AAV above pressure vessel is closed.

Anyway, i replaced a radiator yesterday, but after refilling & bleeding, the pressure is only up to 0.5 bar. The boiler works ok, and when it's up to temperature, it's at 2 bar as usual. but then it drops back to 0.5bar when cold.

I suspect i might have to connect a hose from the mains to valve d?
Also, why is the pressure low if the system is full? i.e all rads bled until water comes out.

Any ideas how to get the pressure up to 1 bar?

Thanks

 

[Dr_Doolittle]

any takers?

 

[penpusher]

you will need to identify, 1, the valve connected to the cold mains and 2, the valve connected to the heating return pipe. Normally there will be a silver braided pipe which connects the two. (although this SHOULD be disconnected after topping up.

 

[Softus]

I don't like the sound of a system that goes from 0.5 bar when cold to 2.0 bar when hot.

Have you checked the pressure in the expansion vessel?

 

[Dr_Doolittle]

no, how can i do that?

 

[Softus]

no, how can i do that?

8th post down on this page: //www.diynot.com/forums/viewtopic.php?t=37170

...and this one too: //www.diynot.com/forums/viewtopic.php?p=569166#569166

 

[Dr_Doolittle]

Thanks for the info. Looks a bit complicated. At the moment valve C is closed so the boiler is only heating the hot water - in which case the pressure ranges from 0.5 to just over 1 bar.

We're due a service in 2 weeks, do you think it will be ok until then?

 

[Softus]

It wasn't my intention to alarm you. I can't tell you that it will be perfectly alright, for obvious reasons, but from the information you've given I can't see a reason for thinking that it will be unsafe.

 

[Dan Robinson]

I can't be a7sed to find the originaly thread, but I remember seeing a small red expansion vessel. How many litres was it and how big is your heating system.

I might suggest a larger vessel.

 

[Dr_Doolittle]

here's the pic you were thinking of:
http://i187.photobucket.com/albums/x228/Dr_Doolittle/DSC00454.jpg

Not sure how many litres it is.

It's just a normal 3 bed semi.

 

[Dan Robinson]

Might well be worth upping the vessel size - I live in a 3 bed house with 5 small - medium double rads, 100 metres on underfloor + cylinder coil in boiler. My vessel is 12 litre.

Yours should have a sticker on it somwhere.

 

[Dr_Doolittle]

Ok, i guess i'll have a word with the boiler guy when he comes to do the service.

Thanks for you help