Radiator not getting totally hot

Hey All
I have a Radiator in the Living Room which is not getting totally hot.
The Radiator was installed a few months ago and has never worked particularly well.
Looking at the Radiator just before the in-flow below the TRV the pipe is very hot, and just after the TRV it is hot but only the top front (double skin) of this big radiator is warm and gets colder towards the bottom.
There is not sludge in the Rad as it has been hosed out
any advice would be appreciated
I have a conventional micro-bore system, with a pump and stored hot water.
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On Sun, 26 Oct 2003 19:58:39 +0000, gna03633

Based on all of this, I suspect that the flow is inadequate for the size of radiator because the pipes are too small.
I assume that you have already bled the radiator of air...??
Do you happen to know the make and type of the radiator? Otherwise, please could you measure it in mm (height and width) and say which type of radiator it is:
- single panel or double panel? - with or without fins? Single panel can be with or without and double can be with no fins or one panel with, the other without or both without.
This will enable looking up the radiator in manufacturer's data to determine the specified heat output.
The water flow has to be adequate to deliver that and microbore may not be. For example, 8mm can deliver 1500W or so of heat over normal distances in a house and 10mm can deliver 2500W.
It may be that this can be resolved by rebalancing the system to increase the flow through this radiator, but before suggesting that, it is certainly worth working out whether the pipes can do the job. If there is a big discrepancy then you would need to upgrade the pipes or use two smaller radiators on separate small feeds.
.andy
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Hey Andy thanks for the reply
The Radiator is 1600 * 600mm (k2?) double panel with fins on both panels - I could pop into the plumber merchants where the plumber bought it and find out the make/btu.
What you say about water flow makes sense, it is furthest from the pump and from where I think the manifold is. I have gotton the radiator hotter with all the other rads in the flat (4) turn off.
Does microbore come in two sizes? It can only supply a max amount of heat if it has the required pressure, so I could have a rad to big for the microbore to ever supply?
I had a hunt for the pump to see if I can increase its rate, there is a lever on it but it was stuck - I didnt want to hit it with a hammer!
cheers gna
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On Sun, 26 Oct 2003 23:41:26 +0000, gna03633

Sorry to be the bearer of bad news but inadequate pipes are the main if not the entire problem.
There is not a huge difference in outputs between similarly designed radiators of different makes. Let's say it's a Stelrad Elite K2, which would be as you describe.
If you go to their web site and download the data sheet, you will find that the heat output in the table is 3626W. This is measured using the EN442 standard which uses test temperatures that are higher than are used with conventional UK boilers. Therefore, the manufacturer includes a derating table and for a conventional UK boiler running at 82 degrees flow and 70 return the mean water temperature is 76 degrees. If the room temperature is at 21 degrees (reasonable) then the mean water to air temperature is 55 degrees, so looking at the table, the radiator should be derated by multiplying the spec.figure by 0.89.
This takes the actual design output for this radiator down to 3227W.
Microbore comes in sizes of 6mm, 8mm, 10mm and 12mm, then the next is standard 15mm hard tube. 6mm is not used a lot because the heat carrying capacity is too small and 12mm is uncommon as well. The two popular sizes are 8mm and 10mm and as I mentioned, over typical distances in a house can carry 1500W and 2500W respectively.
This is arrived at because the tube manufacturers recommend a maximum flow rate to avoid turbulence and hence noise from the pipes of 1.5metres per second.
Heat transfer rate is given by the mass of water x specific heat x temperature difference
- in this case across the radiator. You can therefore calculate a maximum heat transfer rate for a given length and bore of pipe by relating the mass to the volume of water. To a first approximation for lengths of a few metres you can arrive at the ballpark figures above.
If you refer to
http://www.cda.org.uk/megab2/build/Pub150%20UKCB.pdf
there are tables of numbers that you can work through, since the flow is reduced in longer pipe runs.
Following your radiator through the examples, the flow rate required is given by the output in kilowatts divided by 46 and this will be 0.07 kg/sec.
Look at Table 1 and you will see that against 0.07 kg/sec for 8mm tube there is no entry - the pipe is too small. If we look at 10mm pipe, the resistance to flow is 0.192m head per metre of tube.
Now you need to measure the pipe runs. Let's say you have 10m total (add the flow and return lengths) between the manifold and the radiator. To get the required flow rate, the pump would need to be able to deliver the required flow rate and operate at at least 1.92m of head. This is achievable with a typical CH pump.
To do a practical test, you could measure the pipe diameter. If it's 8mm, then I don't think you stand a prayer of making it work and you would need to either upgrade the pipe or substitute 2 smaller radiators searately connected to the manifold.
If it's 10mm and the pipes are not too long, then you are almost within sight perhaps. As you have done, turn off all other radiators and open the lockshield and TRV of this large radiator wide open. The pump normally has a small switch with positions 1,2,3 on it to adjust the output. Try winding it up to full if you can and see if the radiator is getting hot all over. You will probably hear a fair bit of rushing water noise from the system.
If the radiator is still not warming properly then you have inadequate pipe size as before. If it's now OK, try opening the valves to the other radiators a little until they get hot and see if the large one remains hot enough. If so, you could proceed to balancing the system according to the UK.D-I-Y FAQ (look for post by Phil Addison).
If you do get to acceptable settings, you could consider replacing the pump with a Grundfos Alpha. These adjust themselves automatically according to the requirement of the system, increasing and decreasing pressure and flow as required.
However, based on what you've said, my guess is that you will fall short on flow rate through the pipes and need to replace them or change radiators as discussed.
.andy
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Andy Hall wrote:

[SNIP] Not disputing that all that is very sound theory --- BUT .... My largish lounge, as in all the other houses around here built in the 1980s, has such a radiator fed from 10mm microbore. Both halves of the rad get hot and it has for the last 20+ years proved more than adequate to keep the room at the desired 23C even on coldest days ... Also the lounge rad(s) are on the longest run from the CH manifold. Maybe the original "designer" of the system was relying on a higher flow rate than would be considered optimum today.
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BillR wrote:

One simple thing that the OP could do is to put the circulation pump on maximum - we have not been told what boiler he has or where the pump is.
Another work around is to put the boiler to maximum temperature.
The other radiators will need to be strongly controlled with TRV's and/or agressive balancing. [ Wry smile about the discussions we had with you know how about the (supposed) self balancing properties of microbore!]
If neither of these work enough then new flow and return pipes are called for.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
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wrote:

I have a very old Poterton Flamingo 20-30, I have looked at a pump (I have attached a picture which probably breaks some NG rules and proves that I sadly take picture each time I take floor boards up !) and there is a lever at the bottom but is jammed. I didnt want to hit it to hard incase I cracked it!
I will have to re-balance all the other rads
thanks gna
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wrote:

I have a very old Poterton Flamingo 20-30, I have looked at a pump (I have attached a picture which probably breaks some NG rules and proves that I sadly take picture each time I take floor boards up !) and there is a lever at the bottom but is jammed. I didnt want to hit it to hard incase I cracked it!
I will have to re-balance all the other rads
thanks gna
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wrote:

This is within spitting distance because 10mm pipe will carry 2500W typically - not so far short for 3kw if you crank up the pump and balance.
.andy
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Hey Andy thanks again for the time you have spent
I had a look at the size of the Mircrobore in the flat above (dodgy 70/80s conversion!, I see he has 2 manifolds - I'll have to go hunting for mine) and best measurments say its 8mm no matter how hard I try I can't measure it as 10.
So from your great info i'm not going to get the heat from this rad like I do the others. I'll turn off all my rads and see if I can get a bit more heat in it as I know they got unbalance cos of some decorating.
Ultimately I will need bigger pipe since we say 10mm will not really do the job and 12mm is not that common, I will have to go with std 15mm whether this can be joined onto my manifold.
I'll be re-doing the floor in the living room soon so I'll have a look how the pipes run, they run along the hall which I can get the carpet up. Wander how much my plumber will charge for that!, maybe I should ask him why he didn't think of this before he changed the rad ;-(
thanks again
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On Mon, 27 Oct 2003 23:25:03 +0000, gna03633

Generally manifolds have outlets for a given size. You can fit adaptors to go smaller, but generally one size of pipe is used.
For 15mm, you would run it into the 22mm flow and return from the boiler, and then you would reduce the flow down with the lockshield on the large radiator to balanace with the rest.

Ah well........

.andy
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On Tue, 28 Oct 2003 01:15:12 +0000, Andy Hall wrote:

When you hear some describe microbore systems you would think the manifold is some crucial part without which nothing will work. All it is a plumbing fitting for connecting the 8 and 10 mm pipes to the larger pipes that supply the boiler. [Saving a great number of reducing fitting and Ts]
With the advent of flexible plastic pipework in 15mm the main advantage of microbore is no more. The main use of 8 and 10 mm pipework is now to supply gas fires, IMHO.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
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<snip>
<snip>
Ed/Andy,
On that basis could you run two 8mm pipes to and from a rad, and join them to 15mm just before the TRV/lockshield?
I know that running a single 15mm would generally be more sensible, and you would have to have the spare connections on the manifold, just pondering on ways to avoid ripping the microbore out. Presumably (and from your comments) microbore is generally easier to run than 15mm.
In pipe terms, a single large radiator fed by two 8mm pipes might be neater than two smaller radiators each fed by a single 8mm pipe.
Cheers Dave R
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So Dave you are suggesting (partcularly if I have spare 'ports' on my manifold) that I run another (8mm) flow and return microbore and meet them just before my valves.
As Ed mentioned, I did have a hunt around for 12mm microbore but couldn't find any. From what I have read/seen about microbore you can have long runs without joins (seen 25m), and it wont sag under its own weight if no supported.
I could add/upgrade microbore myself taking the floor up and just get my plumber to join my ends (I havent built up my confidence to join pipe!). If I was to run 15mm I would have join lots of bits conners etc.
Anyway my balancing has helped some of the way. But I dont want another rad as I have one large one not getting as hot as I want ;-(
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runs
If
rad
Probably not as firm as 'suggesting' - just putting forward an option which might be a solution. Never having used Microbore (apart from on my computer :-) I am not familiar with the ease (or not) of running pipe compared to 15mm.
It occured to me that 2 * 8mm might give an acceptable flow.
Dredging back to my school days and a bit of Googling, cross sectional area of an 8mm pipe should (using pi r squared) be about 50sq mm. Two 8mm pipes gives you about 100sq mm. A single 15mm pipe gives you about 175 sq mm. A single 12mm pipe gives you about 115 sq mm.
By this very rough calculation - which ignores friction, turbulence, and other arcane stuff - two 8mm pipes should be roughly equivalent to a 12mm pipe in the volume they carry.
I think this should just about heat up your large radiator.
However this needs to be checked by the pro plumbers on this NG.
Cheers Dave R
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On Tue, 28 Oct 2003 22:09:14 -0000, "David W.E. Roberts"

There's no reason why not at all, but to be honest I am not sure of the value.
I had a similar situation where the original builder of the house had just not done the sums on provisioning for a radiator. It wasn't quite as bad as this situation but enough to warrant more flow.
As it happened, I was able, fairly easily to run in lengths of 15mm copper with very little being on show, and then to simply cap off the 8mm pipes near the radiator.

It is, because it is soft. You can bend it nicely with a hand held pipe bender and for going through successive holes in joists it will thread through easily. It's also easy to conceal (e.g.) in electrical trunking or other ways.
However, as Ed says, using plastic is a great way to fit pipework in awkward places and I have done that as well.

.andy
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On Tue, 28 Oct 2003 20:31:34 +0000, "Ed Sirett"

Absolutely true. It is really a convenience and nothing more. It is just as legitimate to connect 8 or 10mm pipe for a single radiator to 22mm main CH pipes if one wants to do so.

It will easily fit in the gaps behind plasterboard so there is some value. Don't forget that 15mm is limited to about 6kW so care has to be taken not to connect too much radiator capacity in branches of 15mm pipes.
.andy
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ooh well, after all the great advice my balancing has made some difference. When the weather gets better I will look at changing the run of pipe, 15mm or 12mm microbore if I could find it. Microbore would be cool as I wouldn;t have to join, or I could learn how to join.
Wait untill I see the plumber again, I'll have a few questions to ask him.
I'll put of rushing to change my boiler to some combi thing, until I have sorted me pipes out
thanks for everyones great advice gna
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Foolish thing to do. Keep the manifold. Have all the flows and returns to all rads from one point. Much better all around.
Tip of the day: Don't take advise from rank amateurs.
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