Rad keeps going cold

[marb]

Ok, last year we had our very very old boiler replaced by a Heatline Combi in the kitchen. There are 5 rads in all. Front dining room, living room 2 x bedroom, bathroom.

When it was first installed all rads worked fine but after a while the front dining room rad went cold, even though it was fully open. I checked to see if it needs bleeding and it doesn't. I turned all the other rads off and gave the boiler a blast with only the dining room rad open. This did the trick and it heated fine, even with all the other rads back on again. After a while the same happens, the front dining room starts getting progressively colder until it no longer heats. The boiler pressure is exactly as it should be. An engineer has serviced it after a year and says it's still mint.

We have another plumber coming round next month to install an additional rad in the kitchen.

Can anyone from experience hazard a guess as to what is happening ?

 

[Whitespirit66]

Has it got a thermostatic valve? May be not working properly. Take head off and see if the rad works. Also, check pin inside TRV moves up and down a few mms.

 

[marb]

No, it hasn't got a thermostatic valve. Just a basic turn on and off knob which works fine.

The rad upstairs in the bedroom has trapped air in the top but I can't bleed it because the tiny screw has rounded. I have tried pliers end even grips to undo the large housing nut it goes into but to no avail. The open and close tap on this rad just goes round and round. I don't want to take the screw out in the centre as I might get flooded. Would new thermostatic valves on all rads better and more economical ?

 

[MarkCharnock]

Try turning the other radiators right down on the lock shield side

 

[marb]

Not sure what a lock shield is, I am assuming it's the capped off plastic on the right hand side ? The two downstairs rads have a tap at each end. It's only the upstairs bedroom rads that have one tap with no lock shield at the other side, the bathroom has no tap and just a lock shield which doesn't move if this helps.

 

[marb]

Can anyone please suggest what may be causing the problem ? I have turned down the left side tap of the rad nearest the boiler but it still hasn't helped.

 

[cantaloup63]

To clarify - you have turned off all the radiators in the house and the one in the dining room is still cold?

 

[xr4x4]

Turn down the smallest and nearest rads to the boiler via the lock shield valve. Turn off completely then open 1/4 turn.

The lock shield valve is the one with the blanking cap on.

 

[xr4x4]

Btw your situation will get worse when the new rad is installed unless your system is properly balanced.

 

[marb]

There are no lock shields on the two downstairs rads, just a tap like the other side. If I turn off all the other rads leaving the dining room open, it comes on ok and carries on for a few days running.

 

[xr4x4]

Lock shield or not, same still applies.

It still needs balancing.

 

[marb]

I have turned down the lockshield on the rad in the middle room to about a quarter. The rad in the front room is still not working though the pipes going to it are hot. They are not blocked or anything as we had them flushed with a high velocity flusher when we had the boiler installed.

 

[marb]

Can anyone help please ? (see above post)

 

[bigpkr]

You say you had the system flushed when the boiler was installed, doesn't mean blockages wont form after a while.

You need to get the system fully balanced, simple.

 

[foxhole]

The seal the tap/lockshield moves can jam so even fully open it sticks shut.
Should have had all vents and valves replaced with boiler if that worn.