We replaced an old downstairs radiator with a new 'designer' version. It's about 5 feet high and looks very good. However - it only warms up about halfway up and not really at its' hottest. We had an 'expert' plumber put it in last Summer. He said get back to him if it doesn't work properly but I really don't trust this guy. The other thing I have found is that our bathroom towel rail radiator doesn't work properly now.
Question - could it be that it's just a case of the water in the radiators not being pumped around enough? I've checked for air in the system and all rads are bled fine. Does the boiler have a pump in it and can one tweak it to make it work harder?
As far as I know the only thing which can cause a rad to get hot at the bottom but stay cold at the top is if the top is full of air. Are you sure you've bled this rad? Have you bled it until water comes out to the bleed valve at the top?
Essentially hot water rises because it is less dense than cold water so as the hot water enters your rad it will go up to the top then across and down again in preference to going straight across to the exit valve. Feel any of your other rads as they warm up and you'll see what I mean. Of course once they are hot the effect is reduced because all of the water in the rad is hot anyway but it's still going on tho some extent.
Lots of other things could be amiss too but none that should cause the cold-top effect. Deal with that first then see where that gets you.
I have bled the new rad. Assuming I'm doing it right - hissing and bubbling water coming out. As far as I know it's a sealed pressure system. The boiler is a Evo HE c22/30.
Bleed valve at the top. Little key with a square end. Hissing as the air escapes followed by a stream of water is right. Don't stop when you get a bit of bubbling/splitting water though as sometimes that can happen before all of the air is out. You should get a stream of water.
If it's a sealed system and you've been bleeding it you will have reduced the pressure. I hope you've topped it up? What pressure is it? It should probably be about 1 bar when cold to about 2 bar when hot.
Also bear in mind that when you've had work done on the system you can end up with air pockets all over the place. The air moves around as the system runs until it settles out in a rad somewhere, strangely there is often one rad in the house where it seems to collect. This leads to you having to constantly bleed one rad until eventually all of the air is out. If this is happening you can probably hear the bubbles moving around the system, especially as they get to the pump as it will get a bit noisey for a second or so.
Have you re-pressurised the system after bleeding? It sounds like you have bled it until you ran out of pressure, rather than you had expelled all the air (same for the towel rail as well). Top up with the filling loop until there is 1 bar of pressure when cold. Then bleed again. Keep topping up and bleeding until all is working as you would expect.
The pressure is reading 1.3 bar at the moment. The system isn't running now as it's been a warm day here and the house isn't cold. The manual doesn't say much apart from keep the pressure between 1 and 2 bar. Presumably bleeding should be done when the system is actually running?
If your having trouble bleeding the system and may have an airlock, this is what I have done.
Set the heating controls so that the heating is on with the thermostat set top max.
Close all the radiators down except for one, I assume they have TRVs. Bleed the one working radiator until you get a jet of water. Make sure all the radiator gets hot.
Open the next radiator and then close the one you've just bled. Bleed this one in the same manner making sure the whole of the radiator gets hot.
Do this for all the radiators.
It's always worked for me except for one time when a radiator hadn't been connected between flow and return and was "inline" gravity fed from the flow pipe. That got me going for a while!
1.3 bar cold is fine (that's system cold not house cold). Ideally bleeding should be done with the system off but it can be done with it on, it's just things can get a bit complicated.
So back to this problem rad, confirm for me it's connected to the system at the two bottom corners and that one top corner has a blanking plug and the other a bleed plug? I really can't see any way it can be hot at the bottom and cold at the top unless it's partially full of air. So it's a case of bleeding it again. Here's what I'd do:
Run the system for a while until the rads are fairly hot. Turn it off. Confirm that the problem rad is hot at the bottom and cold at the top. Note where the boundary is. Bleed the problem rad. Does any air come out followed by water or does it start with water? If it starts with water I'd probably stop and go down the pub. If it starts with air you should feel the boundary move up as the hot water moves up the rad. By the time water is coming out the whole rad should be hot. You might even use this to avoid getting sprayed with hot water - I do. Turn the system on and celibrate. Listen. Can you hear "swooshing" as air moves around? Glugging as bubbles enter the rad and disturb the valve? Give it a while (even weeks) and monitor the rad. If the probelm recurs re-bleed. Don't forget to top up the system if it needs it post bleeding.
The pressure is reading 1.3 bar at the moment. The system isn't running now as it's been a warm day here and the house isn't cold. The manual doesn't say much apart from keep the pressure between 1 and 2 bar. Presumably bleeding should be done when the system is actually running?
NO! bleed when the pump isn't running. I had a system where the suction pressure from the pump stopped the top rad from bleeding properly.
But you might need to run it a bit to shift air bubbles in pipework and let them collect at a bleed point, then bleed, repressurise if necessary, repeat. (But if you do all the radiators in turn the way someone else described, that's less likely to be necessary.)
Another thing to check is that the lockshield valve hasn't been screwed down too much. If you've got poor flow through the radiator, the water could be cooling before it reaches the top of the radiator.
If it ain't that, there may be other reasons for poor circulation in the system, eg. blockage or dying pump.
Sorry Tim but poor circulation cannot be the reason for a rad which is hot at the bottom and cold at the top. Quite the opposite, as the flow rate decreases so the stratification increases with hot at the top and cold at the bottom. The OP may well have poor circulation in the system but as far as I know only air in the rad can cause the symptoms he's describing.
As this is, apparently a "designer" radiator, maybe we should eliminate the possibility that there is some quirk of its design, manufacture, or installation that is causing the trapped air, or otherwise giving this unexpected behaviour.
Wheyhay!!! Things are looking up - radiator is hot at top and bottom now. Did a lot of bleeding and waited until it was just water coming out of the top. I think I was shutting it down when it was still hissing and spluttering. I found that the pressure on the boiler meter was down to 0.9 bar. I've now filled it to 1.5 and when the pump is running it goes up to 1.8.
Thanks again for all your help, chaps.All we need now is some cold weather!
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