Should I open the lever valve a bit to get more flow to my furthest rads?

[D_Hailsham]

I should have said that your boiler does expect a flow/return differential of up to 20C. The higher the differential, the lower the flow so the smalller the pressure loss. In which case the bypass may not need adjusting. Correctly balancing for a higher differential should solve your problem.

What procedure did you follow when balancing the system?

What is the total kW (at 50dt) of your radiators?

Do you know the actual heat loss of your house?

 

[MJN]

The deltaT (difference between flow and return temperatures) ...

Be very careful with this terminology. Whilst the term 'delta T' in the generic sense can refer to any difference in temperature values, in the heating world (and radiators in particular) it usually refers to the difference between the temperature of the room and the average temperature of the radiator.

When referring to 'delta T' across a radiator I'd suggest using the term 'temperature drop' (or similar) to avoid confusion.

 

[D_Hailsham]

Be very careful with this terminology. ... When referring to 'delta T' across a radiator I'd suggest using the term 'temperature drop' (or similar) to avoid confusion.

I was being very careful and was referring to the room/mean rad temperature difference when I asked:

What is the total kW (at 50dt) of your radiators?

I was drawing attention to the fact that the radiator catalogue the OP referred to shows outputs at ΔT = 50C and ΔT = 60C. I was making sure he used the right one. Calculation of the output for smaller ΔTs (and different temperatures/drops) just requires the application of a mathematical formiula.

Radiators are from trads/carron and are victorian style - https://www.tradscastironradiators.co.uk/radiators/cast-iron-radiators/victorian-4-column/

 

[MJN]

I was being very careful and was referring to the room/mean rad temperature difference when I asked:

What is the total kW (at 50dt) of your radiators?

Understood, and it was the use of the same term to describe flow/return difference that has the potential to cause confusion hence me urging caution:

The deltaT (difference between flow and return temperatures)

It's no big deal though; I could just see the confusion creeping in.

 

[Harry Bloomfield]

Thanks muggles

No idea why it's half shut like that. The original installer went bust before commissioning so someone else filled up the rads and commissioned it but didn't have time (inclination?) to do all the balancing. Can't be sure which one of them put the lever at half way, but suspect it was the original installer.

Didn't want to touch it without asking first though in case it was for something important.

Would you suggest just opening it up completely, or just maybe 3/4 open and see if that helps?

Get a sheet of paper, plus pencil and mark the angle before you start - you can always go back to it then. I would start with wide open, just to see if it does in fact make any difference.

 

[pedr0]

Understood, and it was the use of the same term to describe flow/return difference that has the potential to cause confusion hence me urging caution:

It's no big deal though; I could just see the confusion creeping in.

Indeed - the first mention of deltaT did prompt me to search, and the results pointed to difference between average rad temp and room temp. Hence my post #9. But the maths revealed that definition of deltaT probably wasn't the one intended.

What procedure did you follow when balancing the system?

I didn't do anything at the boiler. I opened all valves at the rads, then recorded the order in which the rads heated up. I turned the system off then closed all the rad valves. Then starting at the first rad to heat up, I opened the valve to get a 11 deg drop across rad (measured by putting black electrician's tape on the feed and return pipes and then pointing one of those IR thermometers at the black tape.). Then I moved onto the next rad and repeated until I got to the last ones to heat up.

What is the total kW (at 50dt) of your radiators?

Not sure. I'll track down the original order and figure that out and report back (probably on the weekend now).

Do you know the actual heat loss of your house?

No I don't. I was told by the original installer what heat output I'd need for each room. But I don't know how he calculated that. Contractor has gone bust so I have no way of contacting original installer.

Thank you for all your help everyone. I need to get the figures of my rads and get back to you.

 

[MeldrewsMate]

Average rad temp = (temp at in - temp at out)/2

So if temp in = 70C and temp out = 60C your average rad temp would be (70-60)/2 = 5C ???
A litttle more care with the maths methinks!
Average = sum of components / number of components....I know, I'm just being pedantic.

Or does deltaT just mean the difference between input temp and output temp of a rad. I.e. are you saying that I should be aiming for 20 degrees across the rad rather than 12?

Correct.

On the general point of balancing, all of your ball valves should be fully open. The restriction to flow is set individually on each radiator by its lockshield valve. There is an equivalent usually built into the UFH manifold (adjusted with a bleed key under the electric actuator).
If the lockshield (LS) valve is fully open the flow through that rad is at its highest and the water has little time to lose temperature, therefore the out temp will be closest to the in temp, and the rads average temperature will be at its highest, giving out the most heat.
CLOSING the LS will restrict the water flow, consequently it will dwell longer in the rad so the out temp will be lower, and it's average temp will be lower, and it'll give out (emit) less heat to the room.
It has been suggested that you restrict the water flow though each rad until you get the out temp to be 20C lower than the in temp. That's all you need to do - but remember to do your adjustments with all TRVs fully open, and with all the UFH actuators removed. Usually you'll find one large rad needs its LS fully open, and most towel warmers need just about a quarter turn from closed to get that 20C drop.
Above all, be patient....those cast iron rads are slow to warm, slow to cool.