Combi and New Rads

croman · Posted: Mon Nov 20, 2006 6:21 pm Post Subject: Combi and New Rads

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 · Posted: Mon Nov 20, 2006 7:43 pm Post Subject:

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 · Posted: Mon Nov 20, 2006 8:03 pm Post Subject:

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).

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sime10 · Posted: Mon Nov 20, 2006 8:08 pm Post Subject:

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

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bster · Posted: Mon Nov 20, 2006 9:32 pm Post Subject:

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.

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sime10 · Posted: Mon Nov 20, 2006 9:37 pm Post Subject:

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

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bster · Posted: Mon Nov 20, 2006 10:35 pm Post Subject:

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

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sime10 · Posted: Mon Nov 20, 2006 10:56 pm Post Subject:

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Agile · Posted: Mon Nov 20, 2006 11:53 pm Post Subject:

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 · Posted: Tue Nov 21, 2006 12:02 am Post Subject:

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

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Softus · Posted: Tue Nov 21, 2006 11:43 pm Post Subject:

Agile wrote:

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...