Help balancing radiators, got strange issues

Hi,

Hope someone could point me in the right direction and what I doing wrong.

-Boiler is Vaillant Eco 630 installed last year.

-Radiators were replaced this summer to ultra heat ones.

-11 radiators in total (double) including 2 large single bay windows (2 metre)

I am currently having an issue where two of my radiators in the loft are stone cold if all valves are fully open including one in extension which takes forever to warm up.

I tried to balance but getting very mixed results, turn of the non thermostatic valve and noticed other ones started to heat up including the one is loft but had other issues else where, slowing down.

I bought a 2 channel thermometer from ebay to help me balance and not sure why I get it right.

When does someone need to take the reading? Is it when they have heated up or when just about to get warm? The difference between the two on the first radiator is always above 23-26. I noticed my flow would reach up 55 at one point but return always on 22-25, do I need to open the valve more or close?

Also last night I noticed some of my thermostatic valves were on the return which I believe some say should be fine as mine are quite new. In any case I drained the system and swapped them over so now all are in the correct place.

How do I get balancing using the thermometer, do I start as soon as they warm up in which case one pipe temp is rising rapidly where as other side is still cold?

Is it 12c or 20c for a system boiler like mine?

Any help appreciated, live in NW London if someone free enough and willing to help.

Thanks

when you are balancing, how far do you turn the lockshields from their "closed" position?

I have tried from fully closed to just one turn and all the way.

Just so I understand better, when fully open does it mean the flow will be quicker hence the return should rise in temperature?

This is the first radiator and it heats up super quick on the flow pipe.

Almost all the adjustment is in the first turn or two. After that, it is effectively fully open. So screw it fully shut, and open it half a turn at a time until the flow pipe starts to warm. Once you have found that point, move it no more that a quarter turn each time, and wait 10 minutes before adjusting it again.

You can start with the hottest radiators, but you will have to do them all. After doing them all, go round again doing fine adjustment, but this time wait half an hour between adjustments.

You don't want any radiator to have so much flow that it gets fully hot almost immediately. Flow should be slow enough for the return pipe to be noticeably less hot than the flow.

Any rad that heats up fast is taking flow from the others.

thanks for the tip, will give it a go tonight again.

Does it need to be adjusted when just warming up or can it be done when it has been say stabilised for 1-2 hrs?

for your first adjustment, start from cold and a closed lockshield.

Fine tuning can be hot, but you then need more time to detect the results of your adjustment. Write down "turns from closed" for each valve.

thanks.

do I aim for 12c or 20c difference between the flow and return?

try 20, but if you get enough for all the radiators to heat up at about the same rate, you have cured your problem.

If you have rooms that get too hot because the radiator is bigger than in other rooms, you can turn down its lockshield by a fraction of a turn.