Central Heating System - Forever Bleeding

Sir, determine the height of the system, eg: water column height converted to pressure. Slowly increase the make up water volume and subsequent pressure. Check that expansion device is not water logged. Are all circulating pumps running? Can you read the system pressure at the boiler, usually a tridicator ( altitude, pressure and temperature combo gaging). Be sure that air is not being introduced through the pipimg due to a leaking flange or piping.

These are general checks,

Regards

Hi Mech

Does the system have a header tank, or sealed with accumulator?

If header tank, is it above the highest point in the rad system, now the pipes have been rerouted? Is it full?

If sealed, is it at correct pressure?

Cheers..........Codey

After checking the above.....

Its simply done.... but are you sure the air is bleeding 'OUT' of the bleed valves and not allowing air into the rads????

Also worth checking whether the gas will burn. If there's no inhibitor in the system the rads gradually fill with hydrogen from reaction with steel rads. Seems unlikely, with the amount of gas we're seeing here , but it's a good idea to get some inhibitor in anyway.

Cheers........Codey

The gas is coming out as you can feel it as it does so, I did put a bottle of inhibitor into the radiator that doesn't seem to want to fill, squirted in througha syringe in the bleed valve. The routing is not higher than previously and I think the system has an accumalator, I guess I need to climb around the loft space some more and check the bits that are less easily accessable.

But does it burn?

Codey (not logged on)

Hello Codemaster:

I have not heard of the 'hydrogen' thing before?

Hi babybear, Codey here not logged in, I'm on a strange computer and don't know my details.

Hydrogen is produced from reaction between water and iron in steel rads (if no inhibitor added). It will burn if you open a bleed screw and light the gas. Naturally the reaction also consumes iron and results in leaking rad if left long enough.

Cheers...........Codey

Hello Codey,

Hydrogen is produced from reaction between water and iron in steel rads (if no inhibitor added).

I never knew that! Ignorance is bliss eh? Would that be the cause of the rads going rusty from the inside? I should know about but have never come across it at all. I suppose it would not be a bright idea to light the hydrogen if it filled most of the rad?

Would it 'caboom?'

Take care, and thank you for the post and info! Your not pulling my leg?

A gas can only ignite in the presence of air or oxygen. the test will produce a small blue flame if that is the problem.

The problem is not steel rads in water, its copper piping, water and steel rads, a giant battery!!!

Hello Andy,

do you know, ...........it just never 'clicked'! Of course I know everything and am a Jenious, but never thort of that and it was stareing me in the face for 40 yaers.

Thonk yuo.

No problem Sir, its happened to me and I am sure that many of us have also done a Homer "DUUUUUH" over ourselves when something we should have understood finally clicked into place!

It shows clearly that you are a man of honour, because you even mentioned it!!!

Also, I am glad to be of service in this matter!!!

Have a great day.

Hello again bb

Would that be the cause of the rads going rusty from the inside? Yes, one of the causes.

There is no danger of "caboom", for 2 reasons. The gas inside the rad has no significant oxygen content, so is not flammable as it is, only when it mixes with the air on leaving the bleed screw. Also the jet is travelling faster than the flame can go back into the rad. I've lit it many times with no problem.

It's important to avoid air entry into the system to minimise corrosion, by ensuring there are no points of negative pressure. Also at one time it was common (on systems with header tank) to pipe the cold fill to the boiler return. Due to headloss across the boiler and pipework, this causes "see-sawing" of aerated water in and out of the tank when the pump stops and starts. Better to arrange it boiler - open vent - cold fill - pump - rads, with open vent and cold fill not > 6" apart. It's possible to combine the vent and fill in one pipe but I'm not keen on it.

From a chemical viewpoint, possibly if oxygen does get in there is less hydrogen produced, but it corrodes the rad quicker.

Cheers......Codey

Its common, all plunbers know about it. You need to put a chemical in the water that stops corrosion.....

Wgere are you...

UK central heating systems (especially old ones) are laid out somewhat differently to USA or modern European practice.

My old system was an ablsolute pig to bleed, but when I re-plumbed much ov it I increased the vent pipe to 22mm and made sure it was nice and straight...it's fine now.
The old system had the feed and vent T'd together in such a way that the vent couldn't really work even tho' it was open at the top...so it took ages to fill or bleed.

I remember in one old house I couldn't get a downstairs rad' to fill at all, so I took off the pipe from one side and looked at the ominous surface of the water as it just sat there in the open pipe!
I blew hard down the pip and heard bubble, bubble, gurgle, roar....I snatched the pipe away from my mouth as the jet of water hit the ceiling..I stuffed it back into the valve and bolted it up quick...now that's how to clear and airlock.
Del

Hello Mech:

I had to deal with this as a builder. Someone did there own heating like you and they could not get a radiator to bleed and let in hot water.

I assume you have a system where all pipes are 'going somewhere', IE. there is no pipe that has been left in-line but is not in use?

You must make sure ALL valves in and out of the rads are fully turned on.

You should also check the water pump on the boiler. Some have two speeds. Put the pump on the slow speed then, when you have finished bleeding you can switch to high if you want.

I have been to a house where all connections were 'compression joints', and a joint was hardly tight enough to hold water when the rads were cold. But this joint was not inside the house, think it was in an alleyway? Anyway, no one noticed when it started to let water by when hot and it was also letting a tiny amount of air into the system. So check any compression joints to see they are tight.

I found some thin polyurethane/'nylon' clear tube. And cut 400mm for each Rad'. I found it had to be a good tight fit on the bleed valve.

Then with a towel (to start with) under each rad in turn I opened the bleed valve and pushed the small tube on. With an elastic band round the tube which was folded in half.

I did all rads like this. I put each tube into a bottle and took the band of. Working fast, wait until all signs of air and or cold water are released from the system and start to tighten each bleed valve back up.

It might be easier to get your Family involved, one on each rad?

You can do away with the small plastic tubes if there is someone on each rad. I suggest you are on or near the 'problem rads'. You may need a couple of spare bowls or buckets near the problem rads as the bottles (if you do it that way) may need emptying.

I no this is extreme, and you will have to check the heating top-up tank in the loft has a proper working valve. It may be letting air in? Not all systems have this.

Make sure all is hot and there in no cold bits of the rads themselves.

This has worked for me twice. Do you have any 'airlocks' anywhere else in the cold or hot water to the bathroom and toilet? I know it will not have nothing to do with the heating rads but just wondered. Let me know.

Good luck................

Hello Del,

I grew up before 'yorkshires', no solder then. Well, there was but, only on 'wiped joints' Are, the ole days, going from lead to copper, ah well........ And I learned some tricks from a Family member who was a plumber. I worked with him for a year and it was the best thing I could have done. As you well understand, if you do not 'nip' a joint just tight enough it will loosen from the vibrations of the pump.

When I have been asked to help get rid of what I knew was an airlock, there was at least one in the heating and several in the hot water to the bath and basin. I went it knowing the symptoms and asked the usual questions, have you turned anything on or off in the loft etc, and have to loosened a rad to decorate? The reply was always.........."No mate, would know a boiler if it bit me on the bum"! I always had a length of hose to blow through the pipes. But, why just stand and lie? I don't get it?

I live in a flat now and it is a fully pumped system. Still getting used to it really. I am afraid living on one level is not something I am used to and if there was problem I would know what to do now, but prior to living here in a flat I never worked on any flat ever.

I am typing this by torchlight as the last halogen lamp has just exploded!. So wish me luck!

Take care Del.............

You have had some excellent tips already, but assuming none of them helped, you may need to balance your system properly, before it will drive the air out.

This is true even if it is an accumulator system or one with a header tank (by the way, if you don't even know which of those two systems you have installed, you should not be touching it at all, you are too ill informed and therefore dangerous!).

First check if you have a main bypass valve across the supply and return (to allow some hot water to "bleed" back into the return, to shut down the boiler when hot water is not needed at the rads). This valve needs to be shut and only opened say 1 or 2 turns, if it is open more than this, it will stop the hot water being forced through the rads......by allowing it to bypass them at too high a rate.....

The way to bleed any system is first to let the water cool down, (this is so you can tell which one gets hot water and which do not, simply be feeling the temperature differences with your hand!), then each radiator should have a thermostat at the top and an isolation/balance valve at the bottom. (For top read also inlet and for bottom also read outlet!).

If you do not have this bottom isolation valve, then that is your main problem......you need one also for when decorating, so that you can remove a rad without needing to drain the system completely. Add such a valve to every radiator that you have asap. Forget the rest of this post as without that extra valve, you have a lost cause.....

Ope all isolation valves fully, turn all the thermostats to the highest temperature, start the heating, not which rads get hot water and which do not. Bleed all rads that are cold.

On all the rads that get hot water, close the bottom isolation completely, then open it one tun only!!! No more than one turn. Bleed all rads that are cold.

Now check and find any rads that were cold up to now, that now receive hot water, shut the isolation valve and open 2 turns, not more! Bleed all rads that are cold.

Now see if any of the radiators left now receive hot water, shut isolation valve and open 3 turns. Bleed all rads that are cold.

Continue until all rads are getting hot water.

If any of the rads that were getting hot water start to cool down, open the isolation valve one turn only. Wait and check again after 10 minutes or so.....re-adjust if needed.

If you decorate and remove a rad, remember to cound how many turns the isolation/balance valve was open and note it on the back of the rad. After rad replacement and sealing/connecting, open valve the same amount again.

If you understand simple Ohms law, you can relate this to the radiators, each one is in effect, a resistor connected in parallel across a supply. You need to adjust each one's resistance value so that the same current flows through each resistor, by making them all have the same resistance!!! Simple isn't it?

If you do not understand any part of his, let me know and I will try and help further.

Hello Andy,

some helpful advice there my friend!

Most of our Family were builders and decorators, and, as long as the valves held, we would either take the rad completely off to decorate. Or, loosen the nuts (that hurts sometimes!) push the pipes in to the rad lift it off the bracket and lower it to the floor. Then tighten the connections again.

I know you understand but, I know of no one we worked for (a lot of people!) who had knowledge of how to balance a system, or even what it meant! If you have a place, especially one you own, how to balance the heating, is one of those things you can always make use of? If not yourself then to help friends? But there is always maintenance to do and that )balancing) is one of those things, like simple fuse changing, which is really pretty basic stuff.

Take care Andy.................

You too my friend.

I have balanced many house heating systems using this method, including underfloor central heating as well, it works for any system that I have seen....but maybe I have not seen everything!!

Hello again Andy,

For the way the advice was given..................I give you a GA.

Take care..................

Many thanks.

Thanks for the tips. I've found an acummulator which had its supply turned off, opening this valve seemed to make the pressure continually rise so i turned it off at 2 bar where a settable needle on the gauge had been set. Then all radiators bled in seconds. I still have to check they are getting warm in use, if not I'll try the balancing. But they are all full of water now and with the inhibitor should stop them from creating their own hydrogen supply. I'll check them all in a couple of days for any air that has found its way to the top now it should be running properly.

The systems fairly new though in an old house and when installed by the previus owners (change from wood burner type heating water to Aga style oil fired cooker / boiler) the location of the heat source changed and they seem to have left many existing pipes and tried to use a range of pipe materials and joint types, this seems to be true for for hot water, cold water and central heating systems but I'm slowly tidying up it all as I work through the house.

No other airlocks I know of, though we did a while back get a little water hammer but that seems to have stopped. Had this before elsewhere (gravity fed header tank oon hot water system) but new filler valve that piped the wtaer into the bottom of the tank cured this, after trying many methods of securing / damping pipes and pressure reduction valves etc.

The accumulator should always be in circuit, to even out any pressure changes due to changing water temperature.......let some water out if the pressure climbs too high.....

Yet another thought!!!

When I drained and refilled my system, the pipe supplying water from the header tank was/is almost horizontal!!

So any attempt at bleeding the system was extremely slow and involved taking several days waiting as the air travelled up the tube to the tank very slowly.

The header tank and tube are about 20 feet long and almost horizontal, so an air bubble can take a long time to exit!!

Mech,

I wonder if you mis-connected some pipes?

Is this a gravity circulation system or a pumped system?

It sounds like you don't have a high enough water pressure to fill your system.

Check your fill device for a clogged screen.After 10 years or so they're goners anyway.

Did you trap your pipe runs when rerouting?

BTW...if it takes days for the air to migrate your pipes are plugged.And if your fittings loosen up from pump vibration you need a new pump.

Skies.

Jay.