Some advice needed on draining central heating system

[Mikesoper]

hi all

i have a towel rail with a leaking valve that i intend on replacing . i also have a noisy old boiler that i intend to put some silencer chemicals in. i had this done a couple of years back and it worked well.

can i clarify my steps...

turn off boiler and water supply to header tank
attach hose to drain valve
drain water out
should i turn water back on at this point to flush through a little?
replace faulty valve

should i add chemicals into header tank now and then fill it up or fill tank first then add chemicals?

should i add inhibiter as well as silencer/cleaner? and can this be left in?

bleed rads
boiler on

also if the boiler etc is all off will gravity alone pull water through since pump is off?

all advice gratefully received

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[steadyon]

I would:

1) Turn off boiler
2) Turn of water supply to header tank.
3) Attach hose to drain valve. Other end to foul drain.
4) If S plan, manually open both motorised valves, else set to mid point if Y plan (see note below)
5) Open drain off tap.
6) With care open highest radiator bleed point. Should soon be sucking air.
7) Could open other radiator bleed valves to speed drain. Must open one for rad with valve change.
8) When water below level of valve to be changed, close drain cock. (Unless draining whole system in which case open more radiator bleeds until drain off stops flowing).
9) Change radiator valve.
10) Close drain off tap, close ALL radiator bleed valves.
11) Open supply to header tank.
12) Refill system, bleeding radiators as necessary (and hot water cylinder coil)
13) Check for leaks at new valve.
14) Turn on boiler, get system hot.
15) Check for leaks again.
16) Repeat steps 1 to 6 until header tank empty, then drain two more bucket loads.
17) Add chemicals to header tank.
18) Repeat steps 11 to 13 (or 14 if its cold)

Note that you don't necessarily need to drain the hot water coil circuit, but you will if your towel radiator is on that circuit. If towel rail on on hot water, and your are S plan (two 2 port motorised valves), you might get away without draining radiators. Safest bet is to drain all down below level of radiator valve to be changed.

Good luck.

 

[petercj]

Before opening any drain valves check the header tank for debris - if muck is drained down into the system you could end up with a blocked or restricted heat exchanger in your boiler.

If in any doubt, scoop out the contents of the tank and make sure it's clean.

It's a mucky job, but could save you a lot of money in the long run.