One radiator not heating up

Ashgvas said:
Thanks. I presume it helps to avoid build up of further sludge after a powerflush?
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It will only stop/collect magnetic (magnetite) debris, basically the rust from the inside of radiators etc.. It will not help with other types of debris.
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It's like a small alloy pot, which fits in the return pipe going to your boiler. Down the centre is a sealed tube, where a very powerful magnet fits. Magnetite is magnetic, so it collects around the magnet in the tube. Every so often, you remove the magnet, with the boiler turned off, give the magnetite time to drop away to the bottom of the pots, then open a valve in the base. That release water, and the magnetite with it, then you put it all back together.

I just happen to have given mine a service today, first time in 14 months and it's in fine fettle - barely any magnetite collected, and as usual, the water perfectly clear.
 
old duffer said:
you only ever have magnetite when you have iron. Where is the iron in the average home heating system?
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From the bare steel inside all the radiators, especially so, if the system has spent time with no inhibitor for a time - as is obvious from the OP's mentioned of dark, rusty water.
 
JohnD said:
If you put some X400 in, I bet it would go black as the old sediment is loosened.
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But why would I want to do that, even supposing you were right? I have zero issues with my system, and in the 40 years since install, never have had an issue with the water circuits.
 
terryplumb said:
Is the problem rad one of the original 9 ?? Did it ever work fully ?
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It is one of the original ones. I don't remember exactly, but it was heating slower than the others from pretty much the first few years.
 
old duffer said:
its nothing to do with rust in the pipes, it's a water pressure differential issue which is stopping flow.
Each emitter needs to have a differential across the in/out or flow will not occur. The differential can be very small.
If it is indeed the last in the circuit, you can prove the pressure differential by closing off the a few of the rads. This will force flow and prove the point. Then the balancing is done from this rad. So close all rads and leave this one open, put heating onto full blast. Then start working back towards the boiler in order sequence and keep checking back at the problem rad to make sure its still getting flow.
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Thanks. I tried this technique on Sunday. Shut all the rads except this. Yet it never budged beyond 40 degrees ( I have an infrared thermometer to check the temperature). When I slowly opened the other rads, they quickly jumped to 60 degrees within 10 minutes or so.
 
Harry Bloomfield said:
So, probably the pipework choked up.. The slowest flowing one, so all the debris will accumulate there, making the flow even worse.
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Right, that makes total sense. It's probably the last in the circuit. So had a slower flow anyway and then the debris aggravated the issue.

I also get a lot of gurgling noises in the top radiators despite bleeding them often. One plumber suggested it could be the gases building up due to corrosion. Could that be a thing?
 
Ashgvas said:
I also get a lot of gurgling noises in the top radiators despite bleeding them often. One plumber suggested it could be the gases building up due to corrosion. Could that be a thing?
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Yep, could be hydrogen. Carefully, try a flame to the air bled from a radiator. If it ignites, it is hydrogen.
 
foxhole said:
The valve remaining cold may be faulty , has it been replaced?
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Nope. Haven't replaced the lickshield valve. The valve on the flow side is definitely working- gets hot and regulates flow. The valve on return remains cold. I am wondering that if its the valve - then they'd both get hot?
 
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