No heating or hot water with radiators removed.

[JohnD]

you likely have a blockage in the F&E pipe.

Have you got a strong magnet? Such as a modern pick-up tool?

looking at the pipes in the airing cupboard. There is probably a 15mm pipe coming down from the loft and joining onto a larger pipe. Is that what happens at the points marked "A" and "B?"

how deep is the mud? Brown, is it? Do not stir it up. You don't want it running down into the pipes.

p.s.
there appears to be a valve on the pipe rising from point B. Is that right? Is it closed?

 

[pieceofmind]

you likely have a blockage in the F&E pipe.

Have you got a strong magnet? Such as a modern pick-up tool?

looking at the pipes in the airing cupboard. There is probably a 15mm pipe coming down from the loft and joining onto a larger pipe. Is that what happens at the points marked "A" and "B?"

how deep is the mud? Brown, is it? Do not stir it up. You don't want it running down into the pipes.

p.s.
there appears to be a valve on the pipe rising from point B. Is that right? Is it closed?

Yes I've got a ceramic bar magnet somewhere. What should I do with it?

Yes there's a 15mm pipe joined to a bigger pipe as described.

The 'mud' layer is thin, only really on the walls of the tank. It's brown. Where did it come from?

Yes there's a red tap valve in that pipe. It's open (presuming that fully anti-clockwise is open?)

 

[ianmcd]

As advised where the 15mm pipe connects to the 28mm pipe , try with a magnet, if the magnet attracts to it you have a blockage in there (quite common to happen)

 

[pieceofmind]

The magnet shows gentle attraction in the area of the yellow circle, and stronger attraction in the area of the red circle. What can I do about this?

 

[ianmcd]

would be unusual to block there but very possible, most common place is marked here.

 

[JohnD]

The magnet shows gentle attraction in the area of the yellow circle, and stronger attraction in the area of the red circle. What can I do about this?

I can't see your red circle.

You can Copy and Paste pictures into your post.

It's quite likely that you have a sediment blockage in the pipe, that is preventing the radiators being topped up. This has probably led to insufficient water in the system to circulate, it has air in the top part. That's why water did not squirt out when you tried to bleed the highest radiator in the house. The blockage will have existed long before you saw the fault.

The brown mud is iron oxide, basically rust, from the insides of the steel radiators. Inside the pipes it may be black, and sometimes very hard. As an iron compound it is attracted to a magnet (the black more so than the brown)

If the blockage is in the bend (likely) then the blocked section has to be cut out and replaced with new; or scraped clean and replaced.

Before starting any more work, tie up the ball float in the feed and expansion tank, bale it out into a bucket and remove the water and all the mud. Otherwise more of it may find its way into the pipes, and also squirt out over you when you cut the blocked pipe. Sponge the tank, and lid, and float, clean, and wipe them over with bleach to prevent fungus or bacterial growth in the short term (don't pour it into the tank).

Then look for the main system drain cock, as the whole system should be drained and cleaned to remove residual sediment, or it may block again.

If you are not fond of DIY plumbing, ask around for a local plumber or heating engineer, by personal recommendation from someone whose opinion you value. The fault is very common and any tradesman will have done lots of them.

Website searches are not a good source as the business will usually have paid to be listed, and in some cases can censor unfavourable customer comments.

This pipe is not part of the boiler and is not a gas or combustion part so a plumber can do it who is not a gasman. This might be cheaper, if it matters to you. I know a semi-retired installer who does little jobs like this.

If you have to get a powerflush it will cost you £hundreds, so if you want to save a bit, a DIY clean is worth a try. You will need a cleaning chemical, which is not expensive, and some time.

I am a DIY-ing householder, Ian is a professional and has done lots more of these.

 

[JohnD]

sorry, I said gas. Yours is oil?

 

[pieceofmind]

I can't see your red circle.

 

[pieceofmind]

View attachment 167012 would be unusual to block there but very possible, most common place is marked here.

It is also blocked where you marked it.

 

[pieceofmind]

sorry, I said gas. Yours is oil?

Yep it's oil fed from a tank in the garden.

 

[JohnD]

new pic

The red squiggle there might have sediment in it, but wouldn't be the cause of the problem.

If you have gravity flow to the cylinder, I found that X400 didn't dislodge it, because there is not enough velocity. But in my case, as soon as it was converted to fully pumped, the sludge was washed out from the cylinder circuit and collected in the Magnaclean.

improving your old system is a job for another day. Clearing the blockage and getting it working is more urgent.

I bet Ian's mark is the source of your trouble.

 

[pieceofmind]

improving your old system is a job for another day. Clearing the blockage and getting it working is more urgent.

Wise words. I can cut, clean and resolder if necessary, I just really don't have the time to do it right now. Why don't these problems ever drop when there's a couple of free days and nothing to do lol?

 

[JohnD]

it's not possible to solder a wet pipe unless you can get it perfectly dry. Making up a new joint with compression will be easier, though not so elegant. Also if it ever blocks again you can undo it with a few twists of the spanner.

If you can do DIY plumbing, get yourself a bottle of X400 and circulate it for a month after fixing the blockage, then drain, rinse, and use X100 on final fill.

Can you afford £100 extra for a Magnaclean? (not trying to be impertinent).

 

[pieceofmind]

Making up a new joint with compression will be easier, though not so elegant. Also if it ever blocks again you can undo it with a few twists of the spanner.

Great idea, thank you!

 

[pieceofmind]

Can you afford £100 extra for a Magnaclean? (not trying to be impertinent).

If it saves me having sh*t like this again I'd consider it money well spent. Where should it go?