One radiator not working

[Tom1977]

I've a combi heating system only 4yrs old. all radiators have been working fine until now.
One radiator in the bedroom has ceased to get warm. The trv entrance copper pipe is getting warm and is slowly warming top corner of the radiator.
The exit valve copper pipe remains cold.

I have drained system from pushfit under exit valve. The radiator and valve exits normally. I have also removed valve from radiator and the radiator bleeds freely, making me think there is no blockage. It seems the radiator loop isnt flowing as the hot enters but doesnt continue loop.

Hope this makes sense

 

[terryplumb]

Doesn't make a lot of sense ! Is the pin in the TRV moving up and down freely ? If you undo the TRV from the radiator,and direct it's outlet into a bucket ,or similar ,does water flow freely from the TRV ?

 

[Tom1977]

Pin moves. Both trv and lock shield flows freely when undone

 

[terryplumb]

Turn off the TRV on all rads that heat up ok ,and tell us if the cold rad then heats fully.

 

[Tom1977]

That works. The cold rad after all others trvs are switched off gets hot.

 

[terryplumb]

Turn all the other rads back on , hopefully all will now work. If problem rad ceases to heat the next time heating is put on ,the system needs balancing.

 

[Tom1977]

I've slowly been putting one on at a time. Each time the faulty one has got cooler. What would cause a system to get unbalanced? And how to balance?

 

[terryplumb]

Assuming no plumbing work has been done on the heating system, prior to the rad not working , Altering lockshield valve/s on other rads would alter the system balance

 

[Tom1977]

That's the bizarre thing. Nothing has been touched since system was installed. The combiboiler is used daily. A few weeks ago it did lose pressure.. Maybe a sign for something?

 

[Tom1977]

I've did install a Google nest into the boiler. Maybe this may have had an influence?

 

[Harry Bloomfield]

I've did install a Google nest into the boiler. Maybe this may have had an influence?

No, that would not upset the balance. Balance is one of adjusting the flow, so all radiators get a similar flow through them, despite the variations in pipework, diameters, and sizes. It is done by adjusting the lockshield valves of each radiator, screwing down those with most flow, opening those with insufficient flow.

 

[Tom1977]

I'll have a look at how to do this and try resetting them all. Any tips welcome.

Thanks

 

[Harry Bloomfield]

I'll have a look at how to do this and try resetting them all. Any tips welcome.

Thanks

Beginning with system cold, just firing for first time - Open up the cold one fully, with what were the hot ones fully closed. Reopen them 1/4 to 1/2 a turn, until you feel the flow of heat in them. That should make a good starting point, but read up on how to fine tune the balance.