Old rads all heat up, new ones don't

[nervous123]

As title suggests, all 6 upstairs radiators and 2 downstairs ones which look pretty old get piping hot.

the 4 new ones downstairs installed a year ago get hot at the top but not at the bottom, although the flow pipes get very hot. When bled, the water is clear.

We have never had the system power flushed. A heating engineer advised us not to as we used to have a small leak which he felt had sealed over time and which a power flush would open up again.

Thanks.

 

[petit_pablo]

System needs balancing.

I believe there is a guide how to on the FAQ section.

 

[nervous123]

System needs balancing.

I believe there is a guide how to on the FAQ section.

Is that even though the flow pipe do get hot?

If that's definitely the problem, thanks... I know what I need to do now. I thought the rads might be faulty

 

[MANDATE]

Are the 4 new radiators replacements or has the system been extended.
The reason for asking is that by extending the system and adding more pipe work and radiators there will be more resistance for the water to flow.
So in addition to balancing the radiators you need to consider the setting of the by-pass valve if you have one. The water will not want to go through radiators/pipes if there is an easier route.
If the balancing does not cure it then the pump may be silted up a bit.
I removed a friends pump, only to find silt had reduced the inlet/outlet ports from 20mm down to about 8mm and this explained why a radiator was just lukewarm.