Radiators : out pipe hotter than in pipe

Connacht

Folks,
How come I have a rad with its out pipe hotter than its in pipe ?
The rad itself is barely warm - it's a balancing issue rather than needing to be bled, cos I've already done that. But the inpipe is also barely warm, while the out is hot.
Many thanks.

Merch

assuming the rad is hot/heating up, then I think you may have mixed up which pipe is in and which is out.

Unless there are any other anomalous events occuring in the vicinity of your home? thermodynamic principle defying events, wormholes?

Kidding aside, why do you think the cooler pipe is the input one?

By the by, I'm neither a plumber nor a theoretical physicist.

K.Flyer

May be an air lock problem.
Simple version...
Turn off all other radiators and make sure both of the valves on the problem rad are fully open then turn on the heating system. Have a listen for gurgling sounds at the rad. Leave it run for a while to get good and hot then re open all the other rads and see if it stays hot.

Connacht

Yeah sorry, I was equating the end with the knob with the in-pipe side. Of course, the knob can be on either side, so it's obviously the out pipe side on this rad.
So back to it ...

Merch

The inlet side will heat up first, if even the rad valve for that rad is turned down then it will (should) prevent heat transferring across the rad as there will be no flow through it.
I dont want to undermine the other poster (as I am not a plumber) but before I turned down all valves, I'd try just close the valve on that rad only first of all (thats what I'd do).

When the hot part of the circuit heats up (feeding the inlet to rads) the pipe before the rad should get warm/hot on the inlet side, if you open the adjustable rad valve then (not the balancing valve) the heat should transfer across the rad with the flow of fluid through it, the outlet should then get warm and the rad should get warm across the full height (if there is a cold portion at the top, then the rad needs to be bled of air).

I'm open to correction but I cant see how it could be any other way.
By the way, I wasn't making fun earlier, just in a funny mood

K.Flyer

Merch wrote: »

I dont want to undermine the other poster (as I am not a plumber) but before I turned down all valves, I'd try just close the valve on that rad only first of all (thats what I'd do).

I'm open to correction

If Connacht is not getting enough heat in the radiator (and we are presuming he has no problems with the others) then that means that there is an issue with water flowing through the radiator.
Basic explanation...
The water in a pumped central heating system will follow the path of least resistance, which is why it is essential to have your system correctly balanced so as to have an equal amount of water / heat flowing through the radiators. Now if a rad is not heating up properly with the valves open, trying to close the valve on that radiator, as you suggested, will only stem the flow to it more, thereby not resolving the issue as it most definately will not heat up if the valve is closed.
By closing all of the other rad valves as I suggested and ensuring that both valves on the trouble rad are fully open this will channel the flow of water (increase of pressure) more directly to this problem radiator and if air is trapped in the pipe it will usually dispel it.
At the same time, there could be a build up of sludge in the radiator causing the problem. The same method may dislodge it, but if sludge (black inky liquid) build up is suspected it is better to get a competent Plumber to check over the system and consider having the system flushed clean and balanced properly.

freddyuk

Try unscrewing the inlet valve fully (That is the one with the knob you can turn by hand.) On the outlet side there is probably a cap over the valve with a screw?? Remove the screw and open the valve stem with pliers and see if the water starts to flow hot through both pipes. It will happen quickly if the system is hot already.If it heats up you need to rebalance the system. If it does not get hot then vent the rad via the bleed screw at the top corner. If only water comes out then there is another issue and you need expert advice.

Merch

K.Flyer wrote: »

If Connacht is not getting enough heat in the radiator (and we are presuming he has no problems with the others) then that means that there is an issue with water flowing through the radiator.
Basic explanation...
The water in a pumped central heating system will follow the path of least resistance, which is why it is essential to have your system correctly balanced so as to have an equal amount of water / heat flowing through the radiators. Now if a rad is not heating up properly with the valves open, trying to close the valve on that radiator, as you suggested, will only stem the flow to it more, thereby not resolving the issue as it most definately will not heat up if the valve is closed.
By closing all of the other rad valves as I suggested and ensuring that both valves on the trouble rad are fully open this will channel the flow of water (increase of pressure) more directly to this problem radiator and if air is trapped in the pipe it will usually dispel it.
At the same time, there could be a build up of sludge in the radiator causing the problem. The same method may dislodge it, but if sludge (black inky liquid) build up is suspected it is better to get a competent Plumber to check over the system and consider having the system flushed clean and balanced properly.

What I was suggesting was to stem any flow to that problem rad, so the OP could determine which side was getting hot first, so they know which is the inlet, as the other rads would have flow (none would flow to the problem rad using my method,which I agree would happen), the inlet side of the loop would get hot and they could tell this by touching the pipe at inlet/outlet of the rad and determine which side is on the inlet side of the loop.

To me so long as there is some bypass,As you suggest channeling more water through this rad may help, my method was to determine for the OP which side is the inlet, yours is to help clear any potential blockage.

I agree with you, if they have more of a problem than they can manage in a short space of time they should probably call a competent plumber.