Some cooler radiators

nofoollikeold

1. If the radiator drains freely with both valves removed at their connection to the radiator, then unless the radiator is blocked with sludge, the radiator is OK.
2. If, with the radiator removed, opening each of flow and return (alternately) results in water flowing strongly into a bucket, then unlikely to be a blockage in the system.
3. Which leaves only one or both radiator valves. 
4. I'd suggest:
4a. Take the removed radiator outside, turn it upside down.  Hosepipe from mains at one end and watch the flow at the other end of the radiator.  Repeat with hosepipe in other end of the radiator.  If the outflow on each occasion is roughly the same as the inflow. its not the radiator.  Note: Worth hammering the radiator with a block of wood (on the back) while water flowing to dislodge any sludge.
4b. If radiator not  OK replace it. 
4c. If radiator OK, replace both valves.  Note you will need to drain down to do this unless you can freeze the pipes or know how to "bung" the system.  

looking_forward

A little dark water , but a few months ago I had rad in garden and blasted well and truly with hose - clear running from both sides .... 

I will do this again as not problem with rad off and hit it accordingly  

plumb1_2

looking_forward said:

Before I get further into this I have just removed the radiator that is stone cold . Rad has drained fine and doesn't appear blocked in any way. I have partially opened both valves with a suitable receptacle underneath and plenty of water comes out. When I turn the flow valve on with heating running  a decent flow of hot water comes through. As you may gather I am very puzzled ! 
Any comments much appreciated.

Put the heating on and get the system hot, then turn off. Then repeat opening both valves until hot water comes through.

Bendy_House

LF, I don't think you should open these valves with the system running and with the rad removed; it isn't necessary (water should flow out without the aid of the pump), and opening the LS valve will likely have air drawn in.
If water doesn't flow out JUST under gravity/system pressure (depending on your system type), then I think summat is likely amiss. 

looking_forward

I have opened the valves slightly and then got an assistant to fire the boiler/pump , there is no noticeable difference on the flow although it does get hot . However water still comes down return when pump is running - maybe my understanding is not correct , but I thought with the pump running the return would attempt to draw water ?
cheers 

looking_forward

FaceHead said:

looking_forward said:

Before I get further into this I have just removed the radiator that is stone cold . Rad has drained fine and doesn't appear blocked in any way. I have partially opened both valves with a suitable receptacle underneath and plenty of water comes out. When I turn the flow valve on with heating running  a decent flow of hot water comes through. As you may gather I am very puzzled ! 
Any comments much appreciated.

If the flow is fine, the radiator is fine (I doubt this, I'm in the it's sludged up camp), what happens when you open the return into your bucket? You should get a decent flow of warm ish water returning from the other radiators. 

Ok , so my understanding of the return is incorrect then , if I let flow with pump running I should get a flow out of warm water ? 

plumb1_2

Don’t have the boiler/pump running when pulling the water through 

Bendy_House

looking_forward said:

I have opened the valves slightly and then got an assistant to fire the boiler/pump , there is no noticeable difference on the flow although it does get hot . However water still comes down return when pump is running - maybe my understanding is not correct , but I thought with the pump running the return would attempt to draw water ?
cheers 

It depends... :-)

If this were a gravity system - ie an open F&E tank in t'loft - then the static (ie pump NOT running) water pressure at that valve would just be that 'head' of water, so probably around 0.1bar or so. Ie, not much at all. So, if you removed a rad and opened either valve, water would indeed flow out, but not under any great pressure - you could stop it with a finger. If you then fired up the boiler and pump, almost certainly the flow pressure of the pump would exceed the gravity pressure, so I think you'd find that the 'return' end would draw in air.

That's with a vented system.

However, if your system is sealed - unvented - then it'll be at around 1 bar pressure - that's quite a bit. If you remove a rad and open either valve with this type of system, water will flow out under this pressure as before, but it will be a bit more difficult to stop using your finger - you are likely to get wet trying.

If you now turn on the boiler and pump, this is likely to have little effect on the flow out either valve, since the pump flow pressure will not exceed that of the system's own pressure - water will still spurt out both valves.

BUT, in both cases, when the pump is running, the 'flow' end will always have a greater pressure than the return end, hence water will flow through the rad as it should.

So, what you have experienced is quite normal, and it's extremely unlikely that your plumbing is wrong (do you have a sealed system?). It's more likely to be either a partial blockage, or an unbalanced system - ie some rads are pinching too much flow.

looking_forward

Thanks for the reply - this is a gravity fed vented system with header. I have removed rad again and flushed and whacked. Had a valve on one end and a cork in the other. A small amount of darkish water came out , but nothing untoward. The flow is good and water will stream out of both ends when hose connected.
However , the return does not appear to attempt to draw when the pump is running . The heating on this rad and the living room rad has never been as good as other radiators in the house , I  have balanced and last week I shut down all other rads in attempt to force this one into life.
   Might be relevant - I am also aware that shortly before we moved in a downstairs extension was built and a radiator in the kitchen one removed and 2 more added , I have seen evidence of  a redundant pipe.  
TIA

Bendy_House

If most/all the other rads are shut off, then I WOULD expect the return of this one to 'draw' if the valve is opened with the pump running. These CH pumps are pretty powerful.
If the other rads are 'open', then the draw at this open valve might not be so obvious. ALL a rad needs is a DIFFERENCE in pressure at each end for it to flow; one end doesn't have to be actually 'negative' in relation to atmospheric.
But, since yours is 'gravity', I would expect the return to visibly 'draw' IF it's about the only rad open.
When the rad was fitted and the other rads closed off, did it heat up properly then? I mean, REALLY well, with no issues?
How old is the pump? What speed is it at? Is it noisy?