draining down and refilling CH system

[andyv]

I'm wanting to fit a couple of new radiators on a sealed central heating system, so will have to drain right down.

I'm assuming I just turn off the water, open up at the drain down point and run the water out via a hose pipe, opening up bleed valves as necessary.

When I come to fill up again do I just turn on the pressurising tap on the boiler until it gets to 1.5 bar, then bleed all the air out and keep topping up?

I have some water treatment chemical to go in. Should this go in first before the water when refilling? I'm planning to put it into one of the air bleed vents.

Finally what about the domestic hot water circuit. Is this affected? I presume I can't have hot water with the CH dry. I will turn off the gas and electricity supply to the boiler .

I have a basic idea of how to balance the new rads, but is there far more to it than that?

[John Rumm]

I am assuming you have a combi boiler here (i.e. one that heats the rads and makes hot water "on the fly" with no storage tanks etc) based on your description

Have a look at:

can turn off exiting rads at both ends to save draining those... (note the number of turns to shut off the lockshield, so that you can restore the previously set balancing)

Yup, except there is not need to "turn off the water" (assuming you mean the rising cold main). The filling loop tap ought to be off during normal operation anyway, and there is no other connection between the cold supply and the heating circuit.

Basically. See the FAQ above for a method of refilling on your own. If you have a couple of people then its easy - one goes round bleeding rads and the other keeps topping up the pressure as required.

Yup, if you turn off a rad and slacken a nut connected to one of its tails off, you can drain a few pints out. Then you can remove the blanking plug or bleed valve and pour the inhibitor in. Repalce the plug when done! Keep that rad shut off at both taps until you are sure that there are no leaks in the new pipework. That way you save wasting the inhibitor if you need to drain down again.

That's right - no hot water without the CH circuit working. (although you will still get cold water out of the hot taps even with the boiler switched off.

Not really. A method is described here:

[<me9]

It should be possible to isolate the boiler (and pressure vessel) by closing the isolator valves (if they still work) below the boiler. This will result in losing less water from the system. This saves a complete drain down. I replaced zone valves last week, and only drained out about 3 litres from the system.

Closing off radiator valves at both ends (noting how far open they are so as to reset them after a preliminary bleed) will also restrict the amount to drain out (and put back in).

More or less. Unless three storey I'd only pressurise to about 1 bar.

If you can reduce water loss then it wont be necessary, other wise it will go ine easier first, whilst there is space for it.

It shouldn't be affected.

[Usenet Nutter]

Well surely he won't have any hot water ?

[andyv]

Thanks for your replies.

I got drained down yesterday, and fitted 2 rads and also went round and did a load of TRV's. As John guessed it's a Combi. Until 2 days ago I hadn't been aware of the third type of pressurised system.

I've had to leave it for now and won't be able to fill up until I return next week.