Cold Rads on a system with hot rads

[NODDYNODSVILLE]

Evening all.
I have open vented C/H system with a heat only boiler and 10 rads over 3 floors.
I have just replaced a rad on the middle floor. Drained system down for new gateway valve for cold feed for header tank. Refilled system no leaks, , but the top top 2 rads won’t get hot.
ALL rads contain water, I have bled all rads. No hot water getting to flow pipe of either rad on top floor.
All other rads are working.
When I bleed the top cold rads, all I get is cold water.
Any ideas or help in helping me would be much appreciated
The top 2 rads are run in 15mm. All other rads get hot.
Cold Water actually squirts out of bleed valves in top 2 rads that don’t get hot. These 2 rads are about 10 years old. The others that all work fine are 24 years old.
Any advice would be much appreciated
Simon

 

[Aquarius]

Hi Simon, when you replaced the radiator, did you count the number of turns on the lock shield valve? You may have just upset the balance of the system.

 

[NODDYNODSVILLE]

Hi Simon, when you replaced the radiator, did you count the number of turns on the lock shield valve? You may have just upset the balance of the system.

I believe that rad that was changed, was a by pass rad and had 2 lock shields on it, so I did not count the number of turns. Maybe the system needs balancing. I am a DIY, so not sure how to balance the system

 

[Aquarius]

Ok. Firstly did you put a trv on rad or just change? Secondly try closing valves down all the way both sides and open 1/4 turn. Thirdly have a look here if you’re stuck:

Balancing Radiators Thread.

How To Balance Radiators Tool List: Radiator-bleeding key Lockshield valve adjuster or adjustable spanner Screwdriver Digital thermometer or multimeter with thermometer function 1. Make sure all the radiators have been bled. Turn off the central heating and allow the radiators...

www.plumbersforums.net

 

[NODDYNODSVILLE]

Ok. Firstly did you put a trv on rad or just change? Secondly try closing valves down all the way both sides and open 1/4 turn. Thirdly have a look here if you’re stuck:

Balancing Radiators Thread.

How To Balance Radiators Tool List: Radiator-bleeding key Lockshield valve adjuster or adjustable spanner Screwdriver Digital thermometer or multimeter with thermometer function 1. Make sure all the radiators have been bled. Turn off the central heating and allow the radiators...

www.plumbersforums.net

I bought a new rad, plus a TRV and lock-shield. When you say open 1/4 turn, is that just the lock shield valve.

 

[Aquarius]

I bought a new rad, plus a TRV and lock-shield. When you say open 1/4 turn, is that just the lock shield valve.

Yes, but would have been applicable to both sides of lockshield, I believe @SimonG has advised on your other thread as well, have you tried this?

 

[NODDYNODSVILLE]

Just shut both valves all rads, that are getting hot.
The 2 rads are now HOT, Thanks Simon G for your tip.
Now what do I do.
Not sure about balancing the system., if that’s what it needs.