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How To Balance Radiators

Hot and cold spots throughout your home? Some radiators cold, others hot? They need balancing. It’s an easy job for a DIYer — and our weekend project shows you how with step by step instructions and a full list of tools and materials needed.

Tool List:

  • Radiator-bleeding key
  • Lockshield valve adjuster or adjustable spanner
  • Screwdriver
  • Digital thermometer or multimeter with thermometer function

1. Make sure all the radiators have been bled. Turn off the central heating and allow the radiators to cool.

2. Familiarise yourself with the valves. This is the lockshield. It will usually have a push-on cap or one that is secured with a screw through the top. Remove it.

3. Older models will have a wheelhead valve, like this, on the other side — used to turn the radiator on/off.

4. Newer radiators will have a thermostatic valve like this instead of a wheelhead valve.

5. Open up the valves on all the radiators in the house by turning them anti-clockwise.Wheelhead and thermostatic valves can be turned easily by hand, but the lockshield will need a plastic adjuster to open it up. These come with new lockshield valves. A spanner will also do the job.

6. Turn the central heating back on and note down the order the radiators heat up. Those nearest the boiler normally get hot first. If you’ve got a lot of radiators, get an assistant to help. Turn the heating off and wait while the radiators cool down.

7. When the radiators are cool, switch the heating back on and go to the first radiator on your list. Turn the lockshield valve clockwise until it is closed and then open it by a quarter of a turn. Once the radiator has warmed up, take a temperature reading at the pipework leading to one of the valves.

8. Now take a temperature reading at the pipework leading to the other valve and open the lockshield valve gradually until there’s a 12°C difference between now and the reading you took in step 7 (allow a couple of minutes after each adjustment for the temperature to change). The temperature figures indicated in the last step and this one are relevant to the radiator shown – don’t take them as any kind of optimum figure – it’s the 12°C difference in temperature at the valves that counts. Next, check the rest of the radiators in the system following the order in the list. The further you move away from the boiler, you’ll find the lockshield valve will have to be opened more. The last radiator may need to have the lockshield valve fully open to work at full efficiency. Your radiators are now balanced and should work perfectly.

(MORE: Choosing the Right Radiator)

(MORE: Underfloor Heating or Radiators? Choosing Emitters)

Getting A Temperature

A key part of this job is measuring the temperature difference across each radiator. Specially designed thermometers that strap round the pipes at either end of the radiator are available to buy or hire, but it’s not really necessary to use these. You can get away with a single digital thermometer — it just means that you can’t take simultaneous readings and you’ll have to move from one end of the radiator to the other.

Digital thermometers are available from around £10. Alternatively, some digital multimeters have a temperature sensor function. A digital multimeter with temperature function costs from £25 and can also be used for taking electrical readings and checking continuity in wires, among dozens of other functions.

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26 Comments

Do you know where I can by one from?
Just wanted to say thanks for the instructions. I didn't end up using a thermometer to measure the temperature difference (as I didn't have one that went high enough), but simply closed the lockshield valves on the hotter radiators more than they were already. It takes a while to see the difference, but if you're happy to spread it over the course of the evening you can do it by feel of the radiator. Saved a tenner on not buying a specialist thermometer I'm likely to use once too.
Finally got round to balancing my radiators after reading the how to, which was very clear and concise. Thanks.
Hi to all who read this, i have radiator which i believe is last in the loop to be fed with water, the top is warm not hot and bottom cold/cool, yet all other radiators are uniform with heat, i have drained and removed the radiator turned it on its side to see if any sludge came out also poured water in from one end but to be fair no pressure behind it, and only clear water came out, when draining water it was slightly discoloured but not black. i plumbed the radiator back in again and refilled, plenty of hot water getting through at TRV inlet but on exit at the lockshield its not cold but luke warm,on radiator the inlet you cant touch as its hot but the outlet you can as its cool. I know it maybe down to balance but surely if its pipeing hot going in at TRV it should be the same coming out at lockshield.Any help regarding this would be much appreciated, and for the records all radiators are at the same level.
This is an interesting subject. I had a new house built 4 years ago and the first time the plumbers tested the heating system/radiators all was well but then they had to sort a leak(someone had put a nail through a pipe)and they could never get it right after that,all the radiators were at different temperatures, some would not work at all, bleeding had no effect and no air seemed to come out anyway. The house is a timber frame SIPS built on a concrete slab and the pipes all come down into the radiators from above. When the plumbers came back a few times to try and sort it I used to see them emptying the odd radiator of water for some reason, but I now wonder if it might be worth my while trying to balance the system? By the way these are the same plumbers who arrived on site, emptied a huge bag of fittings on the floor and disappeared for a week or two, drilled the hole for the bath taps in the wrong place, then said for health and safety they can not be fitted at the back, and fitted a pressure reducing valve where the water comes into the house instead of going to the bother of correctly fitting it near the shower(to stop a noise)Thanks for reading my rant, Jim.
Need to try this as the radiators in our house are random upstairs. Anyhows I wanted to know the following ~ Step 5 ~ Open all the valve, does this mean the valves on both sides of the radiator and not just the valve on the inlet side? Step 7 ~ While testing the first radiator should you close the valves on the others or do they remain fully open? Good article once I clarify these few points I'll be giving it a go. Cheers, N
On my upstairs part of the heating system I have two radiators that are about 450mm lower than the rest and they do not get hot at all, can anything be done about it. They are fed from the upper part but separately.
#5 Terry: I just bought a pair in B&Q @£9 ea tried infrared before but found it unreliable
Should the room be up tp design temperature when balancing radiators or should it be cold to mak ethe maximum demand on the radiator.
I've seen this method mentioned many times, but I'm interested if this method is based on: * Folklore * An approximation that's good enough * Some theoretical argument I can't understand - even though I have a science Ph.D. For any give size of radiator, the amount of heat it radiates will depend on temperature difference between inlet and outlet. But it will also depend on the absolute temperatures, which this method totally ignores. If one radiator has an inlet of 42 degrees C, and an outlet of 30 deg C (i.e 12 deg difference), then it will radiate far less heat than one where the inlet is 82 deg C and the outlet is 70 deg C. That is basic physics - Newtons Law of cooling states that the rate of heat loss from a body (i.e. radiator) is proportional to the difference between the body and the surroundings (i.e. the room). This is not an exact, but it is a reasonable approximation. See http://en.wikipedia.org/wiki/Convective_heat_transfer#Equations_.28Newton.27s_law_of_cooling.29 So what theory is behind this method? It looks rather flawed to me, though I concede it might be good enough. But I can think of a better method. Dave
I followed the guide but had difficulties. Firstly I think that my radiaters are not sequential. ie I have at least two radiator circuits. Secondly two of my radiators have thermostatic valves fitted on the inlet side of the radiator therefore the lockshield valve does not control the inlet temperature. Thirdly I have two towel rail radiators with no thermostas but the temperature difference never got as high as 12 deg. It would help if the guide dealt with these issues. I think it would also be clearer to say that you should take the first reading from the outlet valve side as it is the inlet side that will increase in temperature the most. Others have suggested balancing the rads when the thermostats are set at number 3, what do you advise?
Presumably, if I have just one dodgy radiator (the one furthest from the boiler and therefore the last to heat up presumably), I could just open the lockshield a little? Also rather than resetting all the radiators (15 in all I think) I could just check that they are approx 12c difference as described? I suspect that most are "good enough" and would rather fine tune the iffy one. Appreciate that this may be a false economy if I fiddle with values in the wrong order. V.good and interesting read (both article and comments).
This has been something I've been trying to do for ages but never seemed to get it right. Following your article, and with by borrowed temperature probe from work, I've balanced them with no problem. Like all jobs, It's easy once you know how. Thank you.
Step 8 talks about the 12 deg C difference between "now" and the measurement made in Step 7, which is a time-based thing, but parts of the process seem to be talking about this temperature difference being between input and output flows at a point in time. Can someone please clarify? Thank you.
I've just found that the in-ear themometer we use to take our children's temperatures works perfectly well for this job. I wan't sure it would cope with higher temperatures, since it's only intended to measure body temperature, but a quick check with a mug of boiling water allayed my worries.
It doesn't matter whether the lockshield is on the flow or return pipe. Its function is to restrict the flow of water through the rad, not "control the inlet temperature", at least not directly. Just do what the article tells you - measure the temperature of each of the two pipes connected to the rad and adjust the lockshield until you get a 12°C drop. The non-lockshield valve should be fully open, whether it's thermostatic or handwheel.
I've managed to do this before with an infrared thermometer - it worked really well. I got mine from Maplin, but I think you can get them at most electrical goods stores, I'va also seen them on Amazon.
You are trying to allow an amount of water to flow through each radiator to give optimum heat output. When you test for the temperature drop you do not want the possibility of the thermostatic valve closing as the room heats up, so I would open it fully or unclip the thermostatic part of the valve if the room is very warm. Si.
If the room is cold you will need more flow through the rad to maintain the 12c difference, so if you set it when its hot the rooms will heat up slower than if you set it when they are cold. Not sure which is best but you might find if you try and balance it when very cold your system may not have enough heat output to maintain the 12c at the last rads. If you tend to keep the house warm most of the time I would balance at normal temperature as I think the 12c gives efficient use of the hot water in the system. if you balance when cold at normal temps you will have more than 12c difference. Si.
Dr Kirby, The theory is that you are NOT adjusting the heat flow into a room, which will depend on the relative temperature as you say. You are restricting the flow through radiators that have a shorter run, and thus would otherwise "steal" the water flow from radiators that are further away. (May help to think of a set of resistors in parallel, you are balancing them up so each gets an equal amount of current) HTH
Step 5 - Open both valves - if you only open the radiator will not get warm Atep 7 - Leave them open, you are restricting / adjusting the flow in the nearest radiator first. If that is not restricted properly, the fursther radiators will not get the flow anyway.
Thanks Hyman for clearing that up. Regards, Samuel Joy (Online Editor)

An indoor/outdoor thermometer is useful for the in/out water temperature measuring because it has a long wire between the two temperature sensors, so you can measure both sides at the same time.

We have recently had larger radiators fitted at the end of our circuit. These get hot then shut of after 1-2 hours whilst the rads near the boiler at the start of the circuit stay hot

We have balanced the three. THis does not work Does the system need an ancillary pump near the end of the circuit for the three which are going off.

Hello John,

If the radiators are getting hot this suggests the existing pump is sufficient so an ancillary one should not be necessary.

The immediate question is do these new radiators have a thermostat that is kicking in when they reach temperature?

Finally, you need to balance the whole circuit, not just the three. Try this and if you are still having problems it may be worth calling out a professional.

This is not the kind of weather you want faulty heating in, so I hope this works.

Lindsey

Thank you Lyndsay. The "professional" who fitted the new rads is baffled. I have just had another with 3o years experience. He says he is sure that we need to powerflush the system.He did not try balancing and could not explain why if system was ok before it should need a powerflush now.