One hot pipe on radiator but radiator is cold

flyingupthere

ThisIsWeird said:

Albermarle said:

Quite recently I rebalanced our heating as the radiator farthest away from the boiler in a downstairs bathroom took ages to heat up.
After a few rounds of opening and shutting lockshield valves, I mainly achieved my aim.
However suddenly a radiator in an upstairs bathroom stopped getting hot, even when both valves were fully open, although like yours the inflow pipe was getting hot.
After some fiddling about/trial and error, it seemed the lockshield valve was not working properly. After opening and shutting it a few times ( and banging it ) the hot water started to flow again. Now I have not touched it again!
Maybe they can be stuck closed, even though you can turn them ???

Hmm, that's a possibility - the washer could have become detached from the spindle.
Fut, you could first try - open both valves fully, get the boiler running, and shut off a few other rads - just enough to increase flow to the miscreant one. And then thump the control valve body on its side repeatedly with a lump of wood. Not 'hard', but firmly and repeatedly - thump thump thump thump - on the side just where the angle is. Keep feeling the valve body - but mind yer thumbs.

I’m very keen to try this tomorrow, especially before the more dramatic step of taking the rad off the wall.  But - and sorry if I’m being dim here - how will whacking the valve body help the spindle to reattach to the washer if that’s the issue?  Also when you say the control valve do you mean the flow valve (where the pipe is hot) or the lock shield?  Thanks!

Albermarle

flyingupthere said:

ThisIsWeird said:

Albermarle said:

Quite recently I rebalanced our heating as the radiator farthest away from the boiler in a downstairs bathroom took ages to heat up.
After a few rounds of opening and shutting lockshield valves, I mainly achieved my aim.
However suddenly a radiator in an upstairs bathroom stopped getting hot, even when both valves were fully open, although like yours the inflow pipe was getting hot.
After some fiddling about/trial and error, it seemed the lockshield valve was not working properly. After opening and shutting it a few times ( and banging it ) the hot water started to flow again. Now I have not touched it again!
Maybe they can be stuck closed, even though you can turn them ???

Hmm, that's a possibility - the washer could have become detached from the spindle.
Fut, you could first try - open both valves fully, get the boiler running, and shut off a few other rads - just enough to increase flow to the miscreant one. And then thump the control valve body on its side repeatedly with a lump of wood. Not 'hard', but firmly and repeatedly - thump thump thump thump - on the side just where the angle is. Keep feeling the valve body - but mind yer thumbs.

I’m very keen to try this tomorrow, especially before the more dramatic step of taking the rad off the wall.  But - and sorry if I’m being dim here - how will whacking the valve body help the spindle to reattach to the washer if that’s the issue?  Also when you say the control valve do you mean the flow valve (where the pipe is hot) or the lock shield?  Thanks!

Personally I think either valve could be stuck down ( even though they rotate) . In my case it was the lockshield valve, as far as I could work out.
So if it does not work with one, then try the other.

ThisIsWeird

flyingupthere said:

I’m very keen to try this tomorrow, especially before the more dramatic step of taking the rad off the wall.  But - and sorry if I’m being dim here - how will whacking the valve body help the spindle to reattach to the washer if that’s the issue?  Also when you say the control valve do you mean the flow valve (where the pipe is hot) or the lock shield?  Thanks!

It won't help it reattach to the spindle - if it has detached, it'll remain so - but should hopefully help it come loose from where it's stuck, which is blocking off the inlet to the valve, and allow the flow to resume. In which case, it'll now be 'fully' open, and you use the l/s to control the valve from now on.

Yes, I mean the control valve, as that's the one that appears - from your description - to not be letting the water in to the rad.

So, open both valves fully and have the boiler running, as you'll want the water flow to help dislodge the seat if you manage to knock it loose. Then thump :-)

ThisIsWeird

Another simple thing you can try as a test - close the l/s, and open the control fully. With CH running, check the temp of the supply pipe to the control valve - presumably it's warm? Ditto the actual valve body - note the temp. And finally the rad body immediately where the valve joins - ie the first part that would heat up if hot water came in.

Now bleed the valve for a good 30 seconds - make sure you aim into a container! Does the valve body/rad corner heat up?

Albermarle

ThisIsWeird said:

flyingupthere said:

I’m very keen to try this tomorrow, especially before the more dramatic step of taking the rad off the wall.  But - and sorry if I’m being dim here - how will whacking the valve body help the spindle to reattach to the washer if that’s the issue?  Also when you say the control valve do you mean the flow valve (where the pipe is hot) or the lock shield?  Thanks!

It won't help it reattach to the spindle - if it has detached, it'll remain so - but should hopefully help it come loose from where it's stuck, which is blocking off the inlet to the valve, and allow the flow to resume. In which case, it'll now be 'fully' open, and you use the l/s to control the valve from now on.

Yes, I mean the control valve, as that's the one that appears - from your description - to not be letting the water in to the rad.

So, open both valves fully and have the boiler running, as you'll want the water flow to help dislodge the seat if you manage to knock it loose. Then thump :-)

Looking at this useful diagram, I am pretty sure now this is what happened with the lockshield valve on my radiator, which was showing very similar symptons to the OP.
After a few bashes the radiator started getting hot. Since then I have left the lockshield alone. I can still turn the radiator on and off via the flow valve, so that was not the problem in my case.

So I think the OP could have a problem with either valve, although the solution will be the same.

flyingupthere

Albermarle said:

ThisIsWeird said:

flyingupthere said:

I’m very keen to try this tomorrow, especially before the more dramatic step of taking the rad off the wall.  But - and sorry if I’m being dim here - how will whacking the valve body help the spindle to reattach to the washer if that’s the issue?  Also when you say the control valve do you mean the flow valve (where the pipe is hot) or the lock shield?  Thanks!

It won't help it reattach to the spindle - if it has detached, it'll remain so - but should hopefully help it come loose from where it's stuck, which is blocking off the inlet to the valve, and allow the flow to resume. In which case, it'll now be 'fully' open, and you use the l/s to control the valve from now on.

Yes, I mean the control valve, as that's the one that appears - from your description - to not be letting the water in to the rad.

So, open both valves fully and have the boiler running, as you'll want the water flow to help dislodge the seat if you manage to knock it loose. Then thump :-)

Looking at this useful diagram, I am pretty sure now this is what happened with the lockshield valve on my radiator, which was showing very similar symptons to the OP.
After a few bashes the radiator started getting hot. Since then I have left the lockshield alone. I can still turn the radiator on and off via the flow valve, so that was not the problem in my case.

So I think the OP could have a problem with either valve, although the solution will be the same.

Thank you again for all the suggestions.  This seems very plausible to me - however, I've just gone and given both valves a good whack with a hammer, but nothing is happening.

For what it's worth, the pipe ("connection to heating system" in the picture) is very hot.  The nut on it is very hot.  The radiator is a double panel rad and the bit labelled "connection to radiator" is also somewhat hot.  There are also signs of mild heat in the bottom corner of the rad (nearest the pipe) and - barely perceptibly - some heat (I think) at the top of the radiator.  Whacking it seemed to push some of this heat into the rad, but then stop again.  Almost like I whacked it, moved th stuck valve for something to get through, but then the valve became stuck again.

flyingupthere

ThisIsWeird said:

Another simple thing you can try as a test - close the l/s, and open the control fully. With CH running, check the temp of the supply pipe to the control valve - presumably it's warm? Ditto the actual valve body - note the temp. And finally the rad body immediately where the valve joins - ie the first part that would heat up if hot water came in.

Now bleed the valve for a good 30 seconds - make sure you aim into a container! Does the valve body/rad corner heat up?

I just tried this test as well.

Lockshield valve fully closed.  Control valve closed, and bleed valve open eventually leads to nothing coming out of the bleed valve.

Then, opening the control valve fully, water started to flow out of the bleed valve.  (Actually it started almost immediately after half a turn or so.)  I wouldn't say the flow rate was especially strong but it was constant.  One weird thing is it the water would be shooting out in one direction and then suddenly change to another direction (it's not a modern rad with a bleed valve which shoots in a particular direction, it's an older rad where you just unscrew and remove a piece of metal from the bleed valve.)

This seemed to get a mild amount heat into the radiator - it's now a little bit warm across the top.

I'm not sure what this shows!  Maybe the flow rate from the lockshield is so much higher than the flow rate from the control valve (for whatever reason) that in practice no warm water is getting into the rad from the control valve side?

Albermarle

flyingupthere said:

ThisIsWeird said:

Another simple thing you can try as a test - close the l/s, and open the control fully. With CH running, check the temp of the supply pipe to the control valve - presumably it's warm? Ditto the actual valve body - note the temp. And finally the rad body immediately where the valve joins - ie the first part that would heat up if hot water came in.

Now bleed the valve for a good 30 seconds - make sure you aim into a container! Does the valve body/rad corner heat up?

I just tried this test as well.

Lockshield valve fully closed.  Control valve closed, and bleed valve open eventually leads to nothing coming out of the bleed valve.

Then, opening the control valve fully, water started to flow out of the bleed valve.  (Actually it started almost immediately after half a turn or so.)  I wouldn't say the flow rate was especially strong but it was constant.  One weird thing is it the water would be shooting out in one direction and then suddenly change to another direction (it's not a modern rad with a bleed valve which shoots in a particular direction, it's an older rad where you just unscrew and remove a piece of metal from the bleed valve.)

This seemed to get a mild amount heat into the radiator - it's now a little bit warm across the top.

I'm not sure what this shows!  Maybe the flow rate from the lockshield is so much higher than the flow rate from the control valve (for whatever reason) that in practice no warm water is getting into the rad from the control valve side?

To me it shows that the flow valve is working ( partly at least) , the fact that the bleed valve is open, is letting a small amount of hot water into the radiator ( and out again) .
It sounds like if it is a valve problem, the probably the lockshield valve is the problem ( like it was with mine), although could be something else blocking and not be valve connected.

ThisIsWeird

flyingupthere said:

I just tried this test as well.
Lockshield valve fully closed.  Control valve closed, and bleed valve open eventually leads to nothing coming out of the bleed valve.
Then, opening the control valve fully, water started to flow out of the bleed valve.  (Actually it started almost immediately after half a turn or so.)  I wouldn't say the flow rate was especially strong but it was constant.  One weird thing is it the water would be shooting out in one direction and then suddenly change to another direction (it's not a modern rad with a bleed valve which shoots in a particular direction, it's an older rad where you just unscrew and remove a piece of metal from the bleed valve.)
This seemed to get a mild amount heat into the radiator - it's now a little bit warm across the top.
I'm not sure what this shows!  Maybe the flow rate from the lockshield is so much higher than the flow rate from the control valve (for whatever reason) that in practice no warm water is getting into the rad from the control valve side?

Interesting. As Albe says, opening the bleed screw and allowing water out, clearly allows hot water in from the control valve, hence the rad gets warm. So, yes, that does imply that the control valve is at least partly working - opening.

The weird thing is that bleeding the rad with only the l/s open seemed to allow more water out! But, when you look at how these valves work, if the (red) sealing washer is loose - detached - in the l/s, then the water flow through the rad from the control valve would try and push it closed = no heat. But, with the pump not running and the control valve closed, opening the bleed screw would draw water in via the l/s, and this would push the loose washer out of the way. Opening the control valve again, and turning on the pump, would cause the l/s washer to slam shut again.

So, it would seem as tho' the l/s is the valve with the loose washer, and not the control valve with a stuck one! The l/s washer is acting like a one-way valve.

Pure guesswork, of course, but the only explanation I can make fit. I take it that this rad did work at some point? And the plumbing hasn't been changed since then?

Does your boiler have a pressure gauge?

Why did the bleed screw water jet change directions? Teeny bits of debris in the water, coming through the tiny gap and causing slight blockages, making the water change direction, I guess.

FreeBear

If I shut off one or both valves on a radiator here, the valves and pipes remain stone cold when the heating kicks in. The fact that one of the valves on your radiator is getting hot suggests that there is some flow of water through the radiator. If opening up both valves fully is not allowing the radiator to get hot, you have one of three problems -

1. A faulty valve.
2. A serious blockage inside the radiator.
3. A blocked or crushed pipe under the floor.

Draining down the system and whipping off the valves would be the first thing to do. With no water in the system, taking the radiator outside and flushing it through with a hose pipe would be a sensible undertaking. Replacement valves can be had from £16 (Drayton RT212) and Screwfix have a pretty good returns policy if the old valves are OK.