Draining a Sealed System?

[dave12]

Im needing to drain my central heating system! I have a combi boiler and I just want to check I have the right ideas.

My plan is to Turn the Boiler off, connect a hose to the train valve and open it. once the water stops flowing ill open the air valves on the radiators starting from up stairs. once all rads are open and the water has stopped, I can do the job I want to do (fit new thermostat valves on rads).

How do I flush the system? Do I just leave the drain valve open and open the filling valve? The water in the rads is black so I assume the system needs a clean!

I then want to add some anti corrosive stuff. How do I do this?

Once done I then close the drain valve and open the filling valve untill the preesure goes up to ~1.5bar then open the air valves on the downstairs radiators first.

does this sound ok. I don't want to flood my house Thanks for your help

 

[kevplumb]

you can drain the system this way as long as non of the rads you want to work on are drop fed in which case you will have to drain the drops individually
fernox do a cleanser you can inject into a rad then flush out a day or so later
also an inhibitor
refilling sounds fine make sure the auto air vent on the boiler is open tho

 

[Bahco]

You will have to drain each drop.
Suggest you add sludge remover / system cleanser to your system and leave for a week to circulate.
One way of doing it is to remove the cap at the top (side) of rad and screw in a male iron elbow. Place a small funnel in the top and pour in. Do the same with the inhibitor after work is done.

 

[Bahco]

Threads crossed

 

[kevplumb]

yours are

 

[dave12]

Thanks for your answers, just one question to kev plumb. What is the auto air vent, and where will that be?

 

[dave12]

Sorry to be a pain, but does anyone know what the auto-airvent on my combi-boilers is? and where is it?

Thanks

 

[brumylad]

the auto vent is usually a brass fitting shaped like a little mug with a screwed on brass top. Its about 2 inches high and an inch in diameter.

On the top there is a coloured plastic cap. Check the cap is not screwed down tight. If it is unscrew it by about 1 1/2 turns. Don't panic if air hisses out, just waite and check it stops.

the boiler manual may show the position, they are usually at very top of the boiler. often on the left. get out your steps and look down on the boiler

 

[ChrisR]

Quite a lot are insid ea combi, near the pump. Open the front bottom bit and have a look and look for the cap you unscrew. I wonder if the rude-word checker will remove "front bottom" and "unscrew".

 

[kevplumb]

your safe m8 it didnt (morning oilman )

 

[oilman]

I thought you were getting up early, but I suppose it's a different time zone in Thailand.

 

[dave12]

Thanks everyone for your help! The Jobs done, but not without a slight problem.

I replaced my old thermostat valves for Danfoss RAS-C2 Combi valves. When I took the old ones off I realised I coudn't get the nut off the pipe because of a copper ring around the pipe. So I had to use the old nut and old gland (Brass thing that makes the microbore fit into the Valve). This gland never fitted perfectly to the new valve but I didn't know what else to do?
Anyway the systems back up an running now, an although everything is ok, there is a very slow leak on all new valves
What should I do? Can I seal it somehow? or would I be best draining and strating again? If so how do I fit the new glands? What holds them on the pipe?

Sorry if Im sounding dumb, but I just couldn't see how they locked on to the pipe.

 

[brumylad]

old olives can be removed by part cutting through them with a hack saw and then prizing open the slot with a screw driver.

If they have been put on without much pressure you can sometimes knock them off by sliding your adjustable spanner up and down the pipe so it hits the nut behind the olive (hard).

 

[dave12]

Sorry about my lack of knowlege but is an olive the copper Ring that is stopping the old valve nut coming off?

If so then How do I put the new one on? An olive would not be able to hold the new nut on the pipe as the whole is too big, it would just pass over the top?

I think the brass adaptor (gland) must hold it on to the pipe, but how?

Thanks again for your help

 

[kevplumb]

its an insert reducing set
should be three bits one on the pipe
the olive
and the third fits into the valve
paste well if reusing
they can be bought seperatley at the merchants