Seeing John P's earlier questions on central heating reminded me to ask my question 
We have a Worcester Combi boiler with a pressurised central heating system - i.e. no header tank etc.
I need to replace one of the upstairs radiators. The removal and refitting I'm fine with, but how do I go about draining the system and more
importantly refilling it correctly without causing any damage?
Cheers
Nick
There should be a drain at the lowest point of the system, either on a drop next to a radiator, or under the boiler/water cylinder..
Drain as much water out as you need...
Then to refill, there should be a filling point on/under the pressure vessle (expansion tank)... You may need a connecting pipe to join the water
main to the filling point... Technically you are NOT suposed to leave this connected... although we do!
Just open the taps and let water into the system until you get to your predefined pressure... go bleed the rads, and then refill... repeat as necesery
Dont forget to put some fresh inhibitor in the pipework!
I did exactly this when I fitted a new bathroom heated towel rail. I bled the entire system from a downstairs radiator. Trouble is I have no idea
what pressure to keep the system at. As mentioned I have a tap that connects the system to the mains so I can let pressure in a mu Combi boiler has a
pressure gauge. I have been keeping it at 1 bar. But that is a guess, anyone know better?
Whats this inhibitor? Some Anti - rust compound?
OK - sounds simple enough
cue a soaking 
But it may have corrosion inhibitor, you might invalidate boiler warranty if you don't use this.
My "experience" of re-filling a combi boiler system is not a good one. Some crud got into the over pressure value that had obviously
automatically opened at some point (because of air in the system I guess). So bleed rads etc re-pressurized, a week or so latter air had got back into
the system (via the leaky over preasure valve), pressurized it and ruptured the pressure vessel diaphragm, expensive to replace.. Tread carefully,
personally pressurized combi systems seem nothing but trouble to me..
Dan
[Edited on 7/12/09 by Bluemoon]
OR, if your lucky the taps (valves) either end of the rad might hold so you can turn them off undo one carefully to drain the rad into icecream tub
buckets etc
replace rad then top up system bleed rad top up to pressure which of course you noted before you started
also if you only lose a rad full of water the inhibitor shouldnt need replacing
of course if the valves dont hold it will depend on how much they leak and how quick you can remove and relace the rad and obviously how good your
carpet is lol
Ray
ps you can always use a freeze spray to stop the water coming out
[Edited on 7/12/09 by RAYLEE29]
What pressure is your system currently set at?
I would aim for the same or slightly higher...
You could have anything up to about 6 BAR..
Although on an older system I would not want more than 1.5-2 bar.. Wouldnt want to blow it appart.
which worcester is it? some have a plastic key which you insert and half turn into a port to repressurize system, correct pressure should be 1 bar on gauge when system is cold
quote:
Originally posted by RAYLEE29
OR, if your lucky the taps (valves) either end of the rad might hold so you can turn them off undo one carefully to drain the rad into icecream tub buckets etc
replace rad then top up system bleed rad top up to pressure which of course you noted before you started
also if you only lose a rad full of water the inhibitor shouldnt need replacing
of course if the valves dont hold it will depend on how much they leak and how quick you can remove and relace the rad and obviously how good your carpet is lol
Ray
ps you can always use a freeze spray to stop the water coming out
[Edited on 7/12/09 by RAYLEE29]
quote:
Originally posted by t16turbotone
which worcester is it? some have a plastic key which you insert and half turn into a port to repressurize system, correct pressure should be 1 bar on gauge when system is cold
Why are you draining down the system? Is the radiator a different size to the original? Couldn't you just use a freezing kit to isolate any pipes you want to cut and then you only have to fill the radiator not the whole system.
You'll never get the system pressure to 6bar, there should be a 3 bar pressure relief valve built in to the boiler, so a running pressure of 1.5 to 2 bar will be fine.
quote:
Originally posted by neilj37
Why are you draining down the system? Is the radiator a different size to the original? Couldn't you just use a freezing kit to isolate any pipes you want to cut and then you only have to fill the radiator not the whole system.
Check the manual for the system pressure, I think some depend on where the boiler is relative to the highest rad. I think that was one of the problems
I had, as it was a three floors up to the top of the system from the boiler. So to have a positive pressure at the top to allow filling/bleeding you
need a higher pressure..
Dan
did you get it sorted............if not u2u me heating engineer 25 years experance just cant spell