single rad is cold following change of water in the system

[romanrr]

Hi

I'll much appreciate opinions on the following.

• gravity system, two floors
• noise in the pipes best heard in the airing cupboard in the morning. Noisiest on hot water cycle. All rads working fine. attempted to remedy using sentinel noise reducer.
• drained water from the system, added the noise reducer, filled the system with water, bled air from the rads. Effect - no noise, all rads working fine apart from one downstairs - the one through which the system was drained.
• tried shutting valves on all rads apart from the cold one. Effect - bad banging noise (boiling water?) heard in the airing cupboard after about 1 min of running the system with only cold radiator open. Stopped the system to wait until cools down. Opened vales on couple of rads. Effect - system works without noise, the cold rad is still cold.

This rad has the history of having the mind of its own even after cleaning (removed and cleaned). It would start working for no obvious reason.

Any ideas what it could be will be much welcomed.

 

[Gasmk1]

Does it have a TRV, it could be stuck closed if you turned off with it did you open lock shield valve

 

[romanrr]

Does it have a TRV, it could be stuck closed if you turned off with it did you open lock shield valve

Thx. Good point. TRV is on and works fine. Rechecked again - not stuck.

 

[steadyon]

Is the cold radiator on a drop from the floor above?

 

[romanrr]

Is the cold radiator on a drop from the floor above?

yes. the flow and return pipes come through the ceiling straight to the rad. All 3 downstairs rads are like that. Well, two other downstairs rads share flor&return pippes arriving through the ceiling.

 

[romanrr]

sorted.
I reduced flow in two other downstairs rads down to about 1/3 and ... the cold rad started making bubbling noise (as if water coming down) and it turned warm!
I can not find rationale. Ok, i can see the flow has changed after downplaying two other downstairs rads. But I had completely shut flow though all rads yesterday with no effect on the cold rad. Hmm ...
Anyway, it gets warm now. Thanks to all who responded!

 

[Gasmk1]

air locked shutting off other rads force it through

 

[romanrr]

air locked shutting off other rads force it through

Thanks. I tried locking in various combinations - didn't help. Only when I started closing partially in the style when balancing the system. I do not visualize where that air could have been trapped. Really unhelpful not to have the plan of the heating system. That would help to understand the story, i think.