Possible return pipe blockage

[GiGaBaNE]

I am a complete plumbing noob and dont know any terms or names of things yet, but am of reasonable IQ...i think

ok tech specs

boiler; Halstead best70 (placed high on kitchen wall)
Tank; medium sized copper thing with a big red jacket lol ( 1st floor landing)
expan tank; small water tank in the attic (full of manky water when i started)

Problem

I removed the lounge rad to clean it of sludge, also attached a hose to both pipes(drained out the window, not connected to water) to flush out those too. I let them run until the stopped flowing (first sign something was wrong). went up to check the expan tank and discovered the ball cock thing had stuck so i gave it a smack and it now works.

now the radiators dont heat up.
key indicators;
Rads are now clean, but every now and then i will get brown water and a few flakes of black rust pop out of the pipes (i know the brown sludge is from the expan tank and the black is rad rust.

if i hose out the water from the hot pipes (inlet?) they are warm, but when i recconect the rads they stay cold.


i suspect i need to do the hard flush thing from the cold mains but..

where do i connect the hose, downstairs rad pipe?
what happens if i connect to the wrong pipe?
what happens if i connect to the right pipe? lol
what goes in, must come out.....where does it come out?


you can see my dilema. i dont have any cash to spend for a while and i dont want to start ripping up floorboards or some such. hope you can help

note: we plan on a complete central heating system replacement in a couple of years to sell the house, so i just need it to limp through till then.

Interesting side note.
Whilst reading these forums i decided to find the pump (not found it yet afaik) but what i did find was a plug attached to the top of my hot water tank. It has not been plugged in for at least a year (was hidden under the red jacket so i didnt know it existed, i pluged it in and now the tank is making a definate pumping sound), i know it isnt directly related to this specific issue as the heating was working up untill about 48 hours ago. oO

 

[dcawkwell]

My guess is you have an air lock around the pump so the pump is
pumping air.
Find the pump and unscrew the centre nut so if it is turning and it
has water in it.
Any air will leak out when you do this.

Possible places underfloor near back boiler near the pipes (idiots who put
pumps under floor boards).

With the pipes up the wall at the side of the back boiler.

In the airing cupboard at the side of the hot water tank.

Unlikely but possible in the loft.

 

[GiGaBaNE]

dcawkwell...you are a beautiful human being....that was it, right off the bat.

i can now continue flushing the system with confidence! =D


one quick question.
i saw somewhere that i can block the expan tank return, then attach one pipe (from a radiator)to the mains and the the other down a plug hole...

does this work and how effective as a diy flush pls?

FYI: the pump was in a 2nd airing cupboard in the small bedroom. an empty cupboard with just the pump and not a lot else (was buried under storage, lol)