Combi and New Rads

[croman]

I want to move an existing radiator on a combi heated system which will require an extra few meters of pipe. If I turn off the mains cold feed, do I then need to drain down the system. If so and once done, how do I top the system back up. With the bleed valves closed on the rads, will the system re-pressure back to 1 bar when I turn the stop tap back on and open the re-fill loop at the boiler, and then do I keep bleeding and topping up ?

 

[MANDATE]

The mains cold water that goes into your combi comes out as hot water at your taps and the 'central heating' (CH) side is totally separate.
The CH side is filled and pressurised using a 'filling loop' from the 'mains side' Care is needed in filling the CH side, because the mains pressure is high enough to open the 'pressure relief valve'. If you only partially open the valve you can stop the filling as you see the pressure begin to rise and adjust accordingly
You will have to drain the CH side to work on the pipes. After filling you will as you say have to bleed the radiators which will cause the pressure to drop and you need to reinstate that pressure.
I understand pressure relief valves open around 3.5 bar so you could pressurise to say 2.5 bar on the initial filling.

 

[bster]

2.5bar is probably to high for a 'standard' sealed heating circuit probably 1 - 1.5 bar (cold) will then rise to 2 and a bit when hot. Pressure relief probably rated to open at 3bar.

check boiler instructions for charge pressure (if its a combi or system boiler).

 

[sime10]

I think he means 2.5 on the initial filling to bleed rads ?

 

[bster]

fair point, i usually charge to 2bar on initial fill - bleed - fill - bleed, then set the pressure a tad higher than the book states to compensate for loss of pressure due to AAVents.

 

[sime10]

I usually sit by the filling loop and wait for the apprentice to shout
ALL FULL

 

[bster]

I've 'progressed' I used to run around and shout 'full' now i have to man the loop and shout 'full (to myself)

 

[sime10]

 

[Agile]

If you cannot find a suitably qualified apprentice then you have to fit a 1.5 bar pressure reducing valve in place of the filling loop and bleed the rads yourself !!!

Tony

 

[sime10]

If you got an apprentice that can't bleed a rad its time for him or her to go

 

[Softus]

If you cannot find a suitably qualified apprentice then you have to fit a 1.5 bar pressure reducing valve in place of the filling loop and bleed the rads yourself!

...or just run up and down the stairs a lot...