a blocked cold feed/cure?...

[D_Hailsham]

I just closed off my main stopcock which supplies [the F/E tank] and drained from downstairs for a couple of minutes water into my gulley. it came out ok. and the cistern level was the same when i checked.

But if you have turned off the supply to the F/E tank and then drain water from the radiators, the water level in the F/E tank should go down!!

If the level is not going down, the feed pipe from the F/E tank to the heating system is blocked.

 

[liverpoolboy]

sorry another typing mistake, I meant to say when I turned the stopvalve back on it was the same as before. Sorry

 

[D_Hailsham]

I meant to say when I turned the stopvalve back on it was the same as before.

Just to clarify what you mean

You shut off the supply to the F/E tank
Emptied water via a drain valve on a rad
The water level in the F/E tank went down
Turned the F/E supply on
The water level in the F/E tank rose until the ball valve shut off the supply.

Anything wrong with my analysis?

 

[Softus]

sorry it was my fault the way i worded it, making you think I was talking about the cold supply!!

Actually, it was my mistake, not yours. My eyes read the word "system" but my brain saw the word "cistern". I am a fool.

Is there any way I can find out the extend of the blockage/problem etc ?

Only by attempting to clean in various degrees of astringency, and seeing if it works. The problem is, as you already know, that you can't see inside the pipework, so you have to gauge the severity of the corrosion by the colour and consistency of what comes out when you drain it.

For this reason, on the first drain down of a system I'm not familiar with, I pay very close attention to what comes out, which means standing there and watching it until it's finished.

Anything darker than weak tea is indicative of a problem. Black is bad, brown is even worse. This is because magnetite is formed before the corrosive process gets to the point of creating rust. The worst systems contain brown goo that has the consistency of thick tomato soup, or even mud.

I wonder why only the top rads are blocked / sludged up (possibly) and not the bottom floor ones? Maybe they will also get blocked/sludged up over time.

There are many factors. Generally, the faster the flow through a rad, the less gunge will stay in it.

Do you have any TRVs anywhere?

If I flush each rad through in the garden do I just flush through with a hosepipe and mains water?

Yes. Turn it upside down and alternate from each end until it's clean. Empty it between changes.

No cleaner?

Not at this stage.

Should I do the pipework beforehand with the cleaner you recommended?

Yes.