In an earlier contribution to this discussion,
Bob wrote:

Set Square wrote:

It seems to me that your system needs a really good flush out, and
then needs to have inhibitor added. By far the best way to flush it
out - particularly with summer coming on - is to remove the rads and
take them outside and give then a good flush out with a hosepipe.
While they're off, flush the flow and return pipes by keeping the
header tank full and opening each radiator valve in turn (with a
bowl under it to catch the water!). Incidentally, take great care
not to spill any black sludge from the radiators on your carpets -
it makes a pretty indellible dye!

Hi Set Square,

Right, finally had a go at the first radiator....unfortunately the
results weren't as I was expecting from your description.

I took a rad off and flushed it out, and as expected was a bit mucky,
although not really sludgy. I then opened a valve on the pipes (not
sure which is flow and return, so did each separately.) Anyway, when
the pump was off, I got water flowing, which I let run until it ran
clear. However, when I switched the pump back on (by turning up
thermostat) the water stopped flowing and I could feel the suction at
the valve again. The same symptoms occurred at both valves. By the
way, I closed the valves on all other upstairs rads.

Is this what you would expect or is something else wrong.
Additionally, is there anything else I can try?

Many thanks for your assistance.
Bob

Remind me of the original problem - it seems a long time since I wrote the
above!

A description of the system - including the relative position of boiler,
pump, zone valves, etc. would help. Even better if you can take some photos
and upload them to a website and post a reference to them.
--
Cheers,
Set Square
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