One Radiator not getting hot

[bythesea]

Hi all
its that time of week again where ive gotten stuck on a job and could use your thoughts...
flat is in an old folks home all rads piping hot apart from one in living room.
. The pipes to the thermo valve and lockshield were cold when i first arrived altho the vavlves turned on. I took the rad off, emptied and got loads of black water out of it. I opened the valves until water ran hot which it did on both. piping hot like the other rads. I reconnected rad opened it all back up and the rad was nice and hot. Problem was 10 mins later luke warm at best and pipes were cooling.

am i missing something easy? I thought as the water did come through hot that changing the valves wouldnt change anything? There is no boiler in flat as fed from a boiler room which is far away. system must have been vented as was topping self up

so I failed after 2 / 3 hours of messing about. Any thoughts?

 

[Barry98]

Try turning some of th other rads down see if it pumps more heat there

 

[Alex Knight]

Tried balancing all the other rads? Fitted two designer rads last week they only got Luke warm, checked round every single lockshield in the house was wide open

 

[kris]

The pin inside the thermostat will be stuck in, its an easy fix , instead of typing loads heres a link to you tube hope that helps,
https://www.youtube.com/watch?v=kODmE8oXKIo

 

[kris]

Balance , n check pins not sticking , blead

 

[Thedeester1]

What the others said but also try shutting the other radiators too and see if the cold one gets hot.
If its the furthest rad in the system its possible the pump is worn and doesn't have the power to pump water that far when there is a restriction such as the lock shield.

 

[bythesea]

Thanks for the messages
i did turn all the others off to generate more power to this rad but it made zero difference

only thing I could think is that te pin in the thermo valve may be stuck . I had the head off and it opens fully but did not move the pin in the valve itself
What bugs me though is that I hadr the rad working nice and warm then it went cold , I ran the lockshield through and after cold it go red hot then 10 mins later was cooler again . Would that be the pin being stuck ?
This is flat 21 on the end of a run though and it seems other rads in neighbouring flats have similar probs

 

[Hardy1993]

Its got to be the TRV pin sticking down like kris said

 

[Thedeester1]

Well I hope it is the TRV pin. I find it unlikely though, that the exact radiator in other flats all have a sticky TRV pin on the same radiator? Looks more like an air locking issue or flow problem.
I have this in my own house where I have one radiator that will not get hot after a drain down. The hot water will travel the loop quite happily but just doesn't want to go down the radiator leg. After multiple bleeds it eventually works.

Hope you get it sorted!

 

[jtsplumbing]

Either replace pump (What size pump is fitted ?) seems system is struggling , or pipe work is undersized,