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Rads hot on top, cold on the bottom

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  • 10-11-2009 8:06pm
    #1
    Big_Mac
    Closed Accounts Posts: 991 ✭✭✭


    Hi

    My heating system is about 2 years old, and on all the radiators in the house, they are all hot on the top and the remaining 2/3rds of the rad is stone cold. I've drained the system recently but it doesn't seem to have cured the problem. does anyone have any idea of what to do here? I'm a bit lost

    Thanks


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    #2
    Enright
    Registered Users Posts: 943 ✭✭✭Enright


    your rads are 1/3 full of air, there is a litte valve at the top corner of each of them, open this and release the air. Careful as it will smell gassy! It will take abou 3 mins per rad


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    #3
    stedeb
    Registered Users Posts: 264 ✭✭stedeb


    hi mine are the same but as enright says bleeding them may help
    i tried this with mine but no air comes out just water

    is the air trapped at the bottom and you need a tilt on the rads for the air to travel up so it can be released?


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    #4
    stedeb
    Registered Users Posts: 264 ✭✭stedeb


    taken from oter site

    Radiators cold at the bottom

    Why are my radiators cold at the bottom. There is no air in them and they are virtually new as is the combi boiler.
    missieb (Mon 07:44 06/Nov/06)

    Air in central heating. upgrading central heating
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    Answers 1 to 8 of 8



    gasman (Mon 09:02 06/Nov/06) If they are virtually new i doubt the build up of sludge is a problem in the infancy of a system, but it is worth checking the level of inhibitor installed anyway. The problem more than likley is due to poor installation methods, mainley the commisioning side of the installation. If the rads have not been individually ballanced properly then it is possible that the flow is too excessive and does not have time to circulate round the rads before leaving via the return. So i would check each rad for correct ballance first to see if this cures your problem. Best way to check is to take off the tamper proof cap off the return side of the rad valve and with a suitable tool ( small adjustable or grips / pliers ) and turn it anti clockwise. If it will only turn by a small amount say less than one full rotation or even not at all then it has not been balanced and is fully open, allowing the full flow through all at once and resulting in wasted energy and poor ciculation as you describe. If you find this to be true and need to know how to ballance a system then post again. Good luck Gasman.

    missieb (Mon 09:30 06/Nov/06)
    Question Author
    Yes please can you talk me through how to balance the rads. Many thanks for your answer so far.

    gasman (Mon 10:06 06/Nov/06) OK with the heating on full and running for say 1/2 an hour so it should be up to full steam so to speak. Start on your first rad by turning its control valve up to max on the flow side this is the valve that you can turn and probably has numbers on it 5 or max is fully on, or if no indication of which is on then it should be turned fully anti clockwise till it wont go anymore. Then pull off the tamper cap on the remaining valve ( this is called a LOCKSHIELD valve ). Turn it fully clockwise till it is in the off position as posted earlier you will need a tool for this. Once you are happy that it is in the off position then turn it just by half a turn anticlockwise and leave it for a couple of mins and see if the whole rad heats up properly. if not try another half turn and repeat untill the desired effect. Do this on every rad. once set they should never be touched again and the tamper proof cap clicked back into positio. The method i have just described is a bit of guess work and not that accurate but it will work. You will find that the rads closest to the boiler will only need to be opened by a small amount compared to the rads furthest away from the boiler that will need to be set by maybe a couple or more. We actualy use pipe thermomitors to set them a. There should be a difference of 10 degrees C between the flow side and the return side of the rad. And also double check that there is no air left in them by bleeding each rad. Any way Good luck missieb.

    missieb (Mon 10:33 06/Nov/06)
    Question Author
    This is brilliant & I will have a go when the heating comes back on later. Just one thing, does it make any difference to your instructions that all my rads have thermostatic valves on the right hand side?

    gasman (Mon 11:04 06/Nov/06) If you have TRVs (Thermostaic Radiator Valves ) fitted, then turn the knurled collar of the valve ( just under the plastic section of the valve head ) anti clockwise to take the thermostatic head off the valve body. Do this first so that it cannot shut down the rad and spoil your hard work. You will find a small rod/pin type piston that will be sticking up and not stuck down, if it is give it a tap or move it up and down with your pliers till it moves freely but do not pull it all the way out, or you will get wet and the water is going to be very hot !!! When You have balanced the rad and fitting the TRV head again just sit it in position and make sure it is in the max or number 5 position then push it down and locate it by just giving it a twist left and right, you will feel it drop into position then screw the knurled collar back onto the valve body and set it at number 3 then all should be OK again. Best of luck again Gasman.

    missieb (Mon 13:49 06/Nov/06)
    Question Author
    Well Gasman your answers are outstanding. I have printed the whole sequence off & will keep for future reference. Currently I have 2 radiators disconnected while a room is being replastered so I may need to do the exercise again when they go back on. But now I know the cause and the solution. Many Many Thanks. missieb

    missieb (Mon 19:04 06/Nov/06)
    Question Author
    Just to say your diagnosis was spot on Gasman. All the valves were fully open. I've done the balancing (jolly hot job!) and all seems to be fine now. Many thanks again.

    gasman (Mon 21:53 06/Nov/06) Glad to be of assistance to you, happy heating missieb and enjoy :o) .. The Gasman .. (o:

    Answers 1 to 8 of 8


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    #5
    Big_Mac
    Closed Accounts Posts: 991 ✭✭✭Big_Mac


    Ta

    Ok, so far so good. I've adjusted two of the rads and there is a marked improvment, the bottom of both sides of the rad is as hot as the top, but the middle of the bottom of the rad is still cold. Am I doing something stupidly wrong here?


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    #6
    gar_29
    Closed Accounts Posts: 174 ✭✭gar_29


    i have a similar problem. is it a big job to flush the system? i've googled it, and found places that recommend chemical flushing, and others that suggest taking the rads off and flushing them out in the garden with a hose...

    is there a way that is "best practice"? and is it something any plumber should be able to do?

    i reckon the rads in my place haven't been done in ages....


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