How hard is it to drain my central heating?

[Agent L]

I've not got much clue on this and don't want to risk problems but I have a couple of leaky rad valves that need replacing and I'm struggling to find a plumber to do the job (probably my fault for leaving it until this late in the year.

Last time a plumber drained the system he attached a hose to a drain valve on the boiler. What happens at the other end though? It's not a combi-boiler. Do I just shut water off from coming back in? To the tank in the loft or the hot water cylinder?

Or does anyone know of any good online guides how to do it?

My rads are probably 30+ years old so I'm fully expecting the valves to give a bit of trouble when coming off, any tips? I don't really want to replace the rads, but would if I had to, however my main fear is bending/twisitng the pipes that come out of the floor whilst applying force to undo the bottom of the valves.

One final thing, if I don't have thermostatic valves on any other rads is there any point putting them on the two that need replacing?

Edited by Agent L on Friday 15th October 15:02

[shirt]

attach hose to drain plu on boiler or elsewhere in the pipework if you have them. use the one at the lowest point on the system. put the other end of the hose in your outside drain.

open valve.

open bleed valves on all radiators. water now gushes into the drain. if you're just doing the upstairs, you don't need to empty it all.

replace leaky parts.

shut off all the bleed screws and the drain valve. add rust inhibitor via one bleed scre then fill the boiler to 1.5bar pressure using the filling loop.

go round all rads to bleed the air off in each. [i.e. tighten off when water starts to come out with no bubbles]. you will need to add more water as you progress as the pressure will drop with each bled rad.

with all the air out of the rads, open the boiler cover and follow the directions to bleed the air off from the pump. then add more water to get the pressure between 1-1.5 bar.


simple and straight forward.

[Busamav]

But do not forget to first tie the ballcock up in the loft .

[prand]

I had to figure this out pretty quick when I went through a central heating pipe nailing down a floorboard upstairs

At the lowest point in your system, attached to oen of teh heatign pipes, you ought to find a brass tap. You should be able to push a length of hosepipe to it. Mine is quite close to the back door so I ran the hosepipe outside and let the water drain into a drain. I went round the rads after this then let the valves open to let the water clear better.

What the last poster didn't mention is that yuou need to stop water coming back into the system when you do this or you will be draining for ever! Two ways for this - either switch off your mains water at the main stopcock if you don't have a cistern in the loft (combi boilers will be like this). If you have a cistern, you may be able to isolate the water supply in the loft, or do what I did was tie the stopcock up to stop water coming back in if it leaked. You could put a bung in the outlet to stop the whole tank draining, but I didn't have time to sort this out at the time!

Filling back up was a question of closing up all the various rad valves, closing off the bottom tap starting the water supply again (not forgetting to put a bottle of anti sludge in the tank first). And then doing lots of radiator bleeding.

[shirt]

forgot that, but i have a combi boiler with valves on the filling loop, so never needed to do so.


as mentioned, the fun bit is doing it all at breakneck speed when you put a nail through something you shouldn't!

[Agent L]

Cheers guys, you've made it sound pretty straightforward so I'll save myself some money and do it myself.

Would it be a good idea to undo the bottom but on the valve first as a way of stopping the twisting force bending the pipe? I can see myself having to cut off the pipes and having to botch some push fit on or something if it all goes wrong!!

TRVs or not?

[Busamav]

Agent L said:

Cheers guys, you've made it sound pretty straightforward so I'll save myself some money and do it myself.

Would it be a good idea to undo the bottom but on the valve first as a way of stopping the twisting force bending the pipe? I can see myself having to cut off the pipes and having to botch some push fit on or something if it all goes wrong!!

TRVs or not?

There will be NO twisting force on the pipe !

You NEED to hold the valve firm and square with a pipe wrench or similar before you start undoing or tightening any nuts .

[Agent L]

Brilliant, thanks.

[RichB]

As it's an older systems it may have a drian cock lower than the one non the boiler, unless your boiler is on the floor I guess? e.g. my boiler is on a wall in the basement so the drain cock is lower still.

[Agent L]

Yep, should have said, it's a floor standing boiler.

[MJG280]

TURN OFF BOILER before you start so it doesn't fire up.

Close all other rad valves that you aren't replacing then they won't drain down and less hassle to drain and fill. If your rads are upstairs you only need upstairs draining down.


Only use a rust inhibitor Fernox or smilar after you have filled it all up and are sure that your new valves aren't leaking. Wrap ptfe tape round the threaded part that goes into the rad to assist the seal.

Modern rads tend to be different widths than old ones so replacing is another job

[Ferg]

I would make sure you get valves with the correct union size. Taking the tail out of the rad will be a ballache for you. Some are 1/2 BSP, some are 3/4". Filling back up can be a bit of a nightmare, fingers crossed for you!
Incidentally...I wouldn't drain the system at all. I'd bung off the cold feed and vent and drain until the vacuum holds the water.

[Agent L]

Thanks for the inhibitor after checking the system tip MJG280. Very handy.

Ferg, what is BSP?

I got 4 valves yesterday that I'm fairly sure are the right size that means I can leave the tails in. I can always swap them once I have the old ones off tomorrow morning if they are wrong in some way.

One final question, do I need to do anything with the hot water cylinder like turn off the valves that lead to from it or does this need to drain too to empty the whole system?

[RichB]

Agent L said:

Ferg, what is BSP?

British Standard Pipe; it's a thread size like BSF, AF, Whitworth etc.

[cpas]

Agent L said:

Thanks for the inhibitor after checking the system tip MJG280. Very handy.

Ferg, what is BSP?

I got 4 valves yesterday that I'm fairly sure are the right size that means I can leave the tails in. I can always swap them once I have the old ones off tomorrow morning if they are wrong in some way.

One final question, do I need to do anything with the hot water cylinder like turn off the valves that lead to from it or does this need to drain too to empty the whole system?

The hot cylinder only supplied the hot water (taps) and is completely seperate.

[cpas]

Ferg said:

I would make sure you get valves with the correct union size. Taking the tail out of the rad will be a ballache for you. Some are 1/2 BSP, some are 3/4". Filling back up can be a bit of a nightmare, fingers crossed for you!
Incidentally...I wouldn't drain the system at all. I'd bung off the cold feed and vent and drain until the vacuum holds the water.

Hi Ferg.

What would you bung the cold feed with? I have found this sort of thing

http://cgi.ebay.co.uk/PIPE-BLANK-BLANKING-REPAIR-B...

but by tank is too deep to get my arm far enough in.

[-Pete-]

My CH is fed from a small tank, I'd guess a few gallons. Not the main tank in the loft. Find a cork, or as suggested already just tie the ballcock to a stick placed across the top, so it can't drop.

[Ferg]

http://www.draytoncontrols.co.uk/DrainEasyKit.aspx

Although I tend to put a Speedfit cap on the vent pipe rather than the bung.

[cpas]

Thanks for that Ferg. Would one of these work if I wanted to change something on the main water supply (eg change a tap washer)?

[Ferg]

On a tank fed supply, yes.
Obviously for mains cold you just turn it off.