Likely causes of a cold radiator

[srowe]

My unvented system had been struggling for a while so I have powerflushed it. That has cured all but three radiators, they still struggle to heat up. I'm wondering what the probable reasons are

• TRV stuck
• LSV stuck
• blockage in the radiator
• blockage in the pipes

any others? What's the most likely?

 

[ShaunCorbs]

Trv stuck

Take the head off and push and pull the pin up and down a few times

Note when pulling up not no force is required

 

[srowe]

Trv stuck

Take the head off and push and pull the pin up and down a few times

Note when pulling up not no force is required

What's the best way of pushing the pin down, I'm concerned I'll bend or shear it off.

 

[gingalig]

What's the best way of pushing the pin down, I'm concerned I'll bend or shear it off.

It’ll only go down about 10mm, I use a pair of pliers turned side ways so that the surface is flat against the pin. Should move fairly easily and if stuck usually pop back up pretty quick .

 

[townfanjon]

Nact pump
Wrong pipe size
Needs balancing

 

[srowe]

So the pins in all three move up and down freely by about 4mm. Radiator #1 is stone cold, #2 warm at the top. #3 seems ok now, will probably improve once I've balanced the system properly.
I think I'll drain down the system in the summer and take the two rads off and flush them.

 

[Jones82]

If it’s a new build with 10mm plastic pipes, sometimes they are kinked when they cross behind the radiator. You may able to see this by lifting and tilting the radiator forwards. However you may have to remove it altogether and then check the pipes behind.

You could remove the radiator anyway and flush it through with a hose pipe in the garden. Sometimes a powerflush won’t make it round a radiator due to poor flow.