Draining and Restarting a Central Heating System

FrankGrimes

I have to do a bit of plumbing work tomorrow as plumber has let me down (a recurring theme) and it has to be done to allow other work move on.

One job is moving a vertical towel radiator, the other is connecting up some pipes I laid for the extension to the existing heating system.

I’m comfortable with all the mechanics of my compression fittings etc, but I’m not sure how to A) drain the heating system and get the system running again afterwards (i.e. balance it).

I’ll do it with the heating pump turned off, but do I then just fire ahead and disconnect the towel rad and have a bucket in hand to drain it?

The second job is downstairs and involves connecting the pipes I ran in for the extension (all ½ inch qualpex barrier pipe) to the two rads in the extension (not yet fitted – pipes are blanked). I’ll be fitting isolation valves on these feeds but want to connect them now to test for leaks. Can I expect more water to pour out when I remove the blanks from the existing ¾ inch copper pipes that have been left in the ground as feeds for the extension?

When I’m finished to I just connect all the pipes and turn the heating back on and hope for the best? Or do I need to balance the system (how?) and then again when I add the rads in the extension later?

I have some good general DIY books but it’d be great to get a more thorough plumbing book that covers the above and full details of the different types of heating systems. Any suggestions?

SonOfPerdition

FrankGrimes wrote:

I have to do a bit of plumbing work tomorrow as plumber has let me down (a recurring theme) and it has to be done to allow other work move on.

One job is moving a vertical towel radiator, the other is connecting up some pipes I laid for the extension to the existing heating system.

I’m comfortable with all the mechanics of my compression fittings etc, but I’m not sure how to A) drain the heating system and get the system running again afterwards (i.e. balance it).

I’ll do it with the heating pump turned off, but do I then just fire ahead and disconnect the towel rad and have a bucket in hand to drain it?

not unless you want to flood your house, there will be a lot of water iin your rads plus the water in the tank feeding your system . .plus the water that will continue to flow into the tank.

Btw: i'm strictly an amature . .but i've done this in my house quite a few times and i assume your system is similar. But I'm NOT a plumber!

first job is to find point in your system that allows you to drain your system .. may be near your boiler or inside someplace. it should be at the lowest or near the lowest point in the system. Do not drain yey!

Go up into your attic and find the water tank feeding your central heating system. it's usually a small tank near your main water tank. It should have a float in it to feed water into the tank when the level drops. you need to tie up this float to stop water flowing into the tank when you drain the system.

Its sometimes best to use a piece of hose to connect to the drain point to the outside.


Make sure your central heating is turned off and not set on timer.

Drain the system until all the water is drained out.

Now .. you can proceed with your plumbing work. But you will still get water sittingg in the pipes at ground level.

anyhoo . .this is how i do it . . i think this sort of system is called an open system, if it's a closed system then thats a different kettle of fish.

The second job is downstairs and involves connecting the pipes I ran in for the extension (all ½ inch qualpex barrier pipe) to the two rads in the extension (not yet fitted – pipes are blanked). I’ll be fitting isolation valves on these feeds but want to connect them now to test for leaks. Can I expect more water to pour out when I remove the blanks from the existing ¾ inch copper pipes that have been left in the ground as feeds for the extension?

if they are lower than the drain point then you will get some water.

When I’m finished to I just connect all the pipes and turn the heating back on and hope for the best? Or do I need to balance the system (how?) and then again when I add the rads in the extension later?

reconnect your pipes, make sure all work is finished . .then check again . .then . . check again. close the drain point.

you can then start to fill your system through the tank in your attic, just untie the float to start the flow of water .. this may take some time . .i usually carried up buckets of water and filled the tank with the buckets ..but you must be careful .. electrics in the attic, spillage etc.

while you are doing this keep an eye on the areas you worked on looking for leaks. Bleed your rads as the system fills.

once you see the tank is full and not draining into the system you can then switch on your central heating and while it is running check for leaks and continue to bleed if necessary.

I have a bungalow so i'm not sure 100% if your central heating in 2 floors is similar, but i'm guessing the principle is the same.

hope that helps.

crosstownk

SonOfPerdition wrote:

Go up into your attic and find the water tank feeding your central heating system. it's usually a small tank near your main water tank. It should have a float in it to feed water into the tank when the level drops. you need to tie up this float to stop water flowing into the tank when you drain the system.

Good advice from SOP.

You may, however, have a sealed heating system. Instead of a ball valve you will have a loop from you water main to your pressure vessel with a tap on it. This tap is normally off and you should leave it so untill you are finished your work and need to fill the system.

You will need to open rad valves to bleed air out as you fill the system with water

FrankGrimes

thanks for that lads.

I've found the safety expansion overflow outlet on the gas boiler and will connect a flexihose to this to allow me direct it into a bucket. I'm also pretty sure there's an isolating valve on the feed to the cold water tank in the attic so I'll turn this off and then I don't think I'll need to tie up the ballcock.

When I'm refilling do I open all rad valves or just some and do I do this as the system is filling or before I start filling? I assume the purpose is to let air out as the water comes into the system and as each rad valve begins to bleed water I should close them off?

What about balancing the system or can I leave that until the new rads are actually added?

JamesM

The above posts from the others give you most answers.

Also, if you turn off all the rads, (even only one side) you will keep most of the water in the system.

Opening the safety valve on the boiler will not drain the water below that level. I assume that the pipes to the extension are below that level

You almost certainly have a sealed system, so turning off the water to the main cold water tank in the attic will not shut off the supply to the heating system. You have to find a valve, probably in the hotpress, for this purpose.

After you have turned on the water to the system, turn on the valves to the rads and vent the rads one at a time. Do not leave an open vent unattended or you will have water all over the place.

You cannot balance the system until you have all the rads fitted - you may not have to.
Good luck with it.
Jim.

Reyman

If you're draining the system and refilling it one of the risks is getting airlocks in the system, which can be quite difficult to get rid of.
As one of the posters has said leaving the radiators fully open should reduce the risk of this. Also filling it slowly seems to help, so maybe avoid using the buckets and let it fill slowly.

You should also an anti corrosion additive in the filler tank to cut down on deposits and blocking in the system. You can get these additives in any hardware store - Fernox is one I used in the past.

JamesM

Reyman wrote:

If you're draining the system and refilling it one of the risks is getting airlocks in the system, which can be quite difficult to get rid of.
As one of the posters has said leaving the radiators fully open should reduce the risk of this. Also filling it slowly seems to help, so maybe avoid using the buckets and let it fill slowly.

You should also an anti corrosion additive in the filler tank to cut down on deposits and blocking in the system. You can get these additives in any hardware store - Fernox is one I used in the past.

Airlocks are more common in the domestic hot water system than the heating system. The circulating pump usually moves any air into the rads, from where it can be vented.
If you open the rads when draining the system and drain all the water out of the system, you will then have more air in the system when it comes to filling the system again. As I said previously, when you have opened the valve to refill the system - then open the rads ! It can take quite a while to bleed all the rads if they have been completely drained. Also there will be more oxygen in the fresh water that you refill the system with than the old water already in the system and that will lead to more air in the system in the following months.
Fernox is a good idea.
Jim.

crosstownk

JamesM wrote:

Also there will be more oxygen in the fresh water that you refill the system with than the old water already in the system and that will lead to more air in the system in the following months.
Fernox is a good idea.
Jim.

Spot on.

I fitted two motorised valves to my system last November and it took months to erradicate the air. My boiler is in the garage and I had to frequently check the pressure gauge when the system was cold to ensure it was at 1bar. When your bleeding the system be sure to bleed the air vent at the top of the hot water coil.