Airlocked System?

flefla

Alright am currently doing up the kitchen and decided while I had the ceiling pulled off to replace all the old gun barrel pipes on the radiators upstairs since I had easy access to them...so have done this no problem...let the water flow again attempted to bleed the system and nothing so attached a hose from the garden tap directly in and manually pumped water into the system bleeding a radiator at a time until I reached the top of the house and now I've hit a problem....the attic was converted about 10 years ago and there is a radiator up there which is physically the highest point in the system and thats where the block is occuring...so the problem is

1. I attempt to continue pumping water manually into the feed pipe from the ground floor which has worked with every other radiator and nothing happens...out of desperation I switched to pumping water into the return pipe and it worked...radiator in the attic started bleeding air and I thought this was fixed...once I got the radiator fully bled I turned the boiler back on and it tripped out giving a no water flow warning

2. I go back up to the attic and open the bleed valve on the radiator to ensure that it is fully bled and I hear a scream from the back garden and water flies out the overflow pipe and soaks someone sitting out in the sun(if only I had a camcorder set-up) once that finishes bleeding I go back to square one again with no water flow to the boiler and no air bleeding off the radiator but also no water coming off

I've spent in total about 9hours now trying to resolve this so I've tried quite a few different things which are listed below

1. Removed the radiator in the attic from the system completely by closing the stop cocks before the pipes hit the radiator....this resulted in no change...boiler still shows no water flow

2. Closed every radiator in the system that the only place water was flowing was through the pipes...again no water flow through the boiler

3. Reopened all the radiators and started at the top and worked my way down the house bleeding all the radiators as I go...Attic produced nothing...all other radiators bled water...this still made no change and boiler showed no water flow

4. Attemped the process of manually pumping water through again and this time after the radiator in the attic topped up, left it settle for about 10 or 15 minutes turned the water back on and started bleeding more air...did this 2 or 3 times with water periodically shooting out the overflow pipe but still getting the same problem of the boiler showing no water flow

So I am now at a complete loss and hoping someone can help me out with some suggestions...I hope I explained the steps well enough although at this stage I've done so many things so many times that it's all getting a little blurry.

Just to give a bit more info on the system itself it is a sealed heating system with the water tank in the attic which runs to the boiler and then is pumped back up to the radiator in the attic and drops then back down to three radiators on the first floor along with the hot water cylinder and down to another 3 radiators on the ground floor...the overflow would have been installed before the attic was converted so it is on the exact same level(possibly a inch or two lower which is irrelevant) as the top radiator. I do have a diagram drawn out at home so if it will help to provide assistance I can scan it in and upload it later when I get home from work.

One thing I had suggested already this morning was that the fact the overflow is on the same level is causing the problem and to seal it off temporarily and this will allow me finish bleeding the system, at which point I can reopen it

Thanks in advance to anyone who might be able to help

JohnnieK

If it is a sealed system the overflow should not come into affect!!!!! Was it an old open system that was semi-sealed?? This is when the F&E tank is still used as a top up supply but still only has gravity pressure. There is normally a half inch supply coming from this tank into the hot press teeing into the heating pipework with a valve on it. It's possible this valve is open and when you put your garden hose on to the system it's filling up the tank and over flowing. Semi-sealed systems are notorious for air locking. You should seal the system properly if this is the case.

DublinDilbert

You need to figure out what sort system you have, is it a sealed or an open system.

You'll need to figure out how your system fills. When you drained the system, where did you turn off the water from?

It sounds like your pump might be air locked, you should be able to slightly undo the large screw on the top of it to bleed at.

JohnnieK

Dose your heating system have a separate tank to the rest of the house? If so turn off the main at the stop cock. Disconnect the main going to this tank and connect it to the feed pipe to the heating system. Change the valve in the hot press to a filling loop and turn the mains back on. What you have at the moment is a semi-sealed system and they are S***. You now have mains pressure top up. If the problem still persists locate a drain point on the system (radiator, valve or automatic air vent) where you can get a hose onto. Open the filling loop and then then half open the drain point leave running until no air is left. Close the drain and filling loop making sure only 1bar pressure remains in the system. Open the large screw on the face of the pump until water runs free (depending on boiler type the pump might be located inside the boiler). If the the problem is still there I would look at the boiler. If you had the boiler replaced and the system sealed then more than likely it's a system boiler. The have water flow switches inside them and it could be blocked with debris from the system if it is dirty. Try the other thing first and get back to me.

flefla

thanks for all the advice people...it deffinitely is a sealed system although I've eventually managed to figure it out....there is a cylinder in-line with the overflow pipe which is used to trigger the overflow system when pressure is too high in the system...somehow this cylinder had lost all of it's air pressure where it should be at about 2bar...I stuck a tyre pressure gauge onto it and it came up 0 so I drained the system again...pumped this to about 1bar since it didn't have enough resistance to get it higher without spending an hour pumping it...refilled the system from the bottom up bleeding radiators as I went and once the system was full turned on the boiler and hey presto everything worked so I topped up the pressure in the cylinder since it now had enough resistance to easily get to 2bar and the system now works perfectly and has been running fine for about 36hours

thanks again for the advice

JohnnieK

Great stuff. Keep an eye on the expansion vessel! The diaphragm might be perferated if it lost it's pressure.