Draining and refilling combi CH - checking steps

[Hack]

Hi,
I need to replace a couple of radiator valves and want to check on the steps I need to do for draining and refilling the system. I've done a bit of research but want to double-check.

On my lowest placed rad (towel rail style if relevant) which is also installed as a 'stub' off the main system (apologies if the terminology isn't correct), the valves are leaking (lock shield type). I've checked the faq/ wiki and other sources and unfortunately it's not any of the nuts that are leaking. The leaks are coming out of the 'adjuster' thread so I've bought new valves which I need to fit. If relevant I have a valliant ecottec plus 831 combi.
So, to fit I:
1) turn off CH (although not timed to come on) by turning dial right down
2) isolate the ch system but turning off @ the CH flow and return pipes
3) I have a drain cock attached to the CH flow pipe before it hits any rads. I intend to drain off here although there is also a valve on the CH return. Is the CH flow drain cock the right one and the water 'reverse' through the system by gravity as this is the lowest point of the system?
4) once system drained, fit new valves
5) refill system. I have a feeder pipe from the CW mains fill to the CH flow so I assume just open both these up. Is the system full when water comes out of the highest/ lowest rad bleed valve?

And that's it? I don't need to re-pressurise the boiler do I as I isolated it?
Thanks

 

[kevplumb]

1) turn off CH (although not timed to come on) by turning dial right down

turn off the power to the boiler

2) isolate the ch system but turning off @ the CH flow and return pipes

you could they might leak tho

And that's it? I don't need to re-pressurise the boiler do I as I isolated it?

probably will

why bother isolating it at all

 

[bengasman]

Not quite.
Isolate the boiler by taking the fuse out of the spur.( check that it is a 3 amp whilst you are at it)
Leave the heating isovalves alone, good chance they will start to leak if you move them.
You will need to refill to 1 bar after the job is done.
Remember to stick a bottle of quality inhibitor in.

 

[petit_pablo]

Hi,
So, to fit I:
1) turn off CH (although not timed to come on) by turning dial right down
better to switch off on the on/off switch or electrical supply to boiler

2) isolate the ch system but turning off @ the CH flow and return pipes
No need just running the risk of the iso's leaking

3) I have a drain cock attached to the CH flow pipe before it hits any rads. I intend to drain off here although there is also a valve on the CH return. Is the CH flow drain cock the right one and the water 'reverse' through the system by gravity as this is the lowest point of the system?
Go for it although it my take some time, quciker to turn off radiator valves, drain the rad then fit a hose on the end of rad valve and drain from here

4) once system drained, fit new valves

5) refill system. I have a feeder pipe from the CW mains fill to the CH flow so I assume just open both these up. Is the system full when water comes out of the highest/ lowest rad bleed valve?
Repressurise to 1bar ish and bleed all rads

And that's it?
Thanks

 

[Hack]

wow thanks for the quick responses guys!

ok, so I won't bother isolating the CH. I thought I could do that in case I needed/ wanted to use hot water while I'm doing this.
So just switch off entirely instead.

Sorry Bengasman, I knew I'd get the terminology wrong...I meant the radiator in question is not in series ie
boiler CH flow --> rad 1 ---> rad 2 --> etc --> boiler CH return
but there is a T pipe attached to both the flow/ return and the rad is attached to this...not sure if I can draw it but:
boiler CH flow -------> rad 1 ---> rad 2 --> etc --> boiler CH return
| |
v ^
in out
'spur' rad
Do I really need a inhibitor as the system was installed about 4 years ago? Where do I put it in as the system seems closed?

I know there is dump valve as well on the boiler so should I use that too?

Thanks

 

[petit_pablo]

Do I really need a inhibitor as the system was installed about 4 years ago? Where do I put it in as the system seems closed?
Yes inhibitor is always needed, especially on newer boilers where water quality is vital to them working properly. Remove 1/2" cap from top of radiator/towel rail and pour it into the radiator before you refill

I know there is dump valve as well on the boiler so should I use that too?
No no no

Thanks

 

[kevplumb]

I know there is dump valve as well on the boiler so should I use that too?

View media item 14379

 

[bengasman]

Spur as in "electric supply thingy on the wall" that has a fuse in it somewhere.
Yes, inhibitor in it. Always. Whenever the system has been drained. Even brandnew system needs it. Very hard to have too much inhibitor. Too little kills the boiler, the rads and the valves.

Don't touch the "dump valve" I presume you mean the prv.

 

[bengasman]

For general ch understanding, somebody on here had a really clever way of putting it.
The flow and return of the boiler are connected to a ladder, the rungs are the rads. Bearing in mind that the pump moves the water at a rate of 0.5 metres every second, the difference between the "first" and the "last" rad getting warm is usually not much more than half a minute. IF the system is designed and installed correctly that is.

 

[Hack]

ok thanks guys!
so I WON'T touch the dump valve
hmm interesting tho as a couple of engineers have both used that to drain the boiler when doing other work on it (fitting replacement pressure sensor see //www.diynot.com/forums/viewtopic.php?t=160809)
Also where someone recommends isolating CH...
I WILL use inhibitor

On spur thing...def not the electrical definition of spur...is there not a plumbing definition where a rad is not part of the in/ out of the ch flow and return but has been added on using a T connector on the ch flow/ return pipes?

 

[Hack]

ok just seen the ladder definition. I thought the system was in series. ladder analogy makes it a lot clearer!
thanks