2 metre long rad won't heat up

[Nige F]

2 metre rad ....2 metre post FFS

 

[D_Hailsham]

That diagram would be easier to assimilate if you quoted the flow rates in litres per minute.

Why? Can't you multiply by 60?

I think that you are making an assumption that the flow rate from a boiler varies.

Why do you think I am assuming that?

All boilers vary their power output and the system flow rate is usually constant.

Correction. All modulating boilers vary their power output.

If the power output is reduced, then the flow rate should be reduced proportionately. But, as you say, in many cases it does not, particularly if the rads just have wheel valves. But if they have TRVs, these will have closed down. So the differential pressure will have risen and the flow rate reduced. Whether this reduction is proportional to the reduction in power output is another question.

As I said ages ago the flow through a rad is set to provide the temperature differential the boiler requires.

Purely convention. It assumes that the radiators have been sized so they give out the exact amount of heat. If the radiator is oversized, this can be countered by increasing the differential, which reduced the power output.
You could do the same for undersized rads, but you do not have the same flexibility as with an oversized rad.

As long as the differential at the boiler is correct, the differential across a radiator is irrelevant.

 

[tonybhoy]

EAGA, the government backed free heating systems set-up for people over 60 in Scotland, only fit rads with TRV (flow) at the top of the rad and the LS (return) on the bottom however I believe they do this because of the age of the home owner so that they can use the TRV easier.

 

[DIYedboy]

I did it because it was a direct replacement, however, the original was the first rad on the circuit, after repiping the system the correct way to get rid of pumping over, it has become the last on the circuit, the flow speed must now be a lot less and so I'll have to put the lockshields at both ends (bugger)

 

[Nige F]

Did you tell anyone that in the first place .Or do you just like winding up gas fitters

 

[D_Hailsham]

I did it because it was a direct replacement, however, the original was the first rad on the circuit, after repiping the system the correct way to get rid of pumping over, it has become the last on the circuit, the flow speed must now be a lot less and so I'll have to put the lockshields at both ends (b*****r)

Now you tell us!

The system needs proper balancing. With the last rad in the circuit being probably the largest, balancing will be critical.

See How to Balance a CH System.

 

[DIYedboy]

Nige................you're a saucy boy aren't ya?...........,my last post does not affect the original question, which those learned, experienced and HELPFUL plumbers/gas fitters kindly answered (thanks again)..............Anyone using this site to learn something rather than run the gauntlet from the petty minded that just want to extract the urine will now know that a 2metre rad should not be plumbed in on one side cos it's highly likely to give problems irrespective of flow speeds or the rad's position within the system.