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. | | PlumbersForums.net

Find Balancing Radiators Thread. Advice and Help. How-to Balancing Radiators Thread. in the Plumbing Jobs | The Job-board advice boards on PlumbersForums.net | Plumbing Advice for All. Balancing Radiators Thread.

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. | | PlumbersForums.net

Find Balancing Radiators Thread. Advice and Help. How-to Balancing Radiators Thread. in the Plumbing Jobs | The Job-board advice boards on PlumbersForums.net | Plumbing Advice for All. Balancing Radiators Thread.

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.