draining rads to try and solve prob, but tank still full

[ribs]

Hi all, I hope someone can help.
We found that we had a problem with the radiator upstairs, only the bottom half was getting hot on most and two were not getting hot at all. Radiators downstairs were working OK.
After spending a few hours trying to bleed them, we still did not have water in the top of the radiators. I thought that we might have a problem with sludge so I bought some Fernox cleaner.
Then things really got confusing... I'm an electrical engineer, not a plumber, electricity is so much more prodictable!! I found a drain connection next to the pump downstairs, connected a hose to it and opened it up. We got lots of black, thick water out of the system but when I checked the smaller of the two tanks in the loft when the water had stopped, it was still full.
So where do I put the fernox cleaner now!!? Could it be that I have a blockage between the tank and the first radiator? If so, how do I clear it?

 

[hi-spec plumbing heating]

if you have a blockage it will be where the 15mm feed joins the system.

 

[ribs]

Thanks Hi-spec for the quick reply... Ive had a look at the piping coming from the tank and from what I can make out (theres very little room up there) the water leaves that tank in 22mm, then reduces to 15mm just before dropping down though the ceiling to the 1st radiator.
These are to two radiators that dont even get warm at the bottom. The pic below is how I think the piping is laid out, but this would mean that the water would have to flow though atleast one of these radiators to raech the others.. could this be right?

 

[hi-spec plumbing heating]

not really. your rads should be connected to return pipe work to your boiler.

your tank feed should connect near your pump. in the airing cupboard

 

[ribs]

mmmm.. didn't look right to me either, maybe it was installed by another electrical engineer! The pump is downstairs not in the airing cupboard, sort of behind that backboiler but in the kitchen. The pump has a 22mm on one side which I think goes to the boiler (this is the one with the drain that I used to 'drain' the system with) the other side has a 22mm pipe that disappears into the wall and also a 15mm 'T' that goes to the nearest radiator. This other side of this radiator goes back into the cupboard where the pump is, turns into 22mm and again disappears into a wall.., I think this is the return.

If the radiators are connected across the feed and return pipes, what is at the end of the run? Are the feed and return pipes connected together to complete the 'circuit' or is there a radiators across the two ends?

 

[hi-spec plumbing heating]

http://s213.photobucket.com/albums/cc142/hispec/?action=view&current=2.gif

 

[ribs]

Thanks Hi-spec......... I'll have a closer look in the morning and see if I can find the blockage one last time before calling in a professional.

 

[hi-spec plumbing heating]

can you see one of these

http://www.screwfix.com/app/sfd/cat...HZPCFFA?productId=31421&imageNo=null&ts=85083

 

[ribs]

no... dont think we have motorised valve anywhere. On the heating controller you can select water only or heating and water, but not heating only.

 

[hi-spec plumbing heating]

sounds like gravity water pumped heating

 

[ribs]

yep... one other thing too...... looks like we have lost our hot water too (wife is not happy!!! ). Had to use the immersion. Does this narrow down where the blockage could be??

 

[JohnD]

Use your immersion heater if you have one

The blockage will be in the feed, it always is. If the primary circulation is partially empty because the F&E is not filling it, then there will be insufficient water to circulate to the cylinder coil. You could do a temporary fill by putting a hosepipe on the drain cock and filling until your highest radiator bleed valve emits water. Fill it from a hot tap, if you use mains water pressure and have a blockage you may cause leaks or other damage.

The blockage will be be why you had the initial problem; also why the F&E tank won't empty; also why the cleaning chemical will not work as it can't flow down the blocked pipe to reach the blockage.

You might be able to find the place where the blockage is by holding a strong magnet against the copper pipe, you will be surprised to find it is attracted to the copper at one point, probably the first Tee. This is because the black sludge is composed of the iron from your corroded steel radiators, and is Magnetite. You can cut out this Tee with the blockage, and then all the water remaining in the F&E tank will gush out (so syphon it out first) and the black will cause an indelible stain.

I bet you can cut out that Tee, put a new one in, and then use your chemical cleaner, which wil loosen the hardened sludge and let it flow round in the circulating water. You can use some of the money you saved on plumbers costs to buy and fit a Magnaclean in the return pipe to the boiler, you will be amazed and gratified at the amount of black sludge that it traps. It will cost you about £100. As an amateur, i did one in the summer; it cost me an Sunday afternoon to do the initial drain and fit (including several new drain-off valves) and another afternoon a couple of weeks later when the Magnaclean had stopped gathering large amounts of additional sludge to drain and refill with inhibitor. The magnet will carry on trapping circulating black indefinitely and only takes a few minutes to empty.

I am not a plumber

 

[ribs]

Thanks Hi-spec, and JohnD you have convinced me to have one more bash at it tomorrow before admitting defeat.

 

[Softus]

The blockage will be in the feed, it always is.

Actually, it isn't always the cold feed tee; I'd estimate about 19 out of 20 times.

 

[wilhelm]

also , look for one of these.

if found. ..