Radiator not heating up

boongywoongy

We have two radiators on either side of a wall between our lounge and kitchen. They seem to be both connected to two vertical pipes (one is hot to touch whilst the other is worryingly cold) on the lounge side. Whilst the lounge radiator (on the grey wall) is luke warm the kitchen side (on the white wall) is cold. The pipe leading to the trv is hot but the entry point into the radiator remains cold. I believe the trv has been changed but it hasn't helped. I've bled the radiator and also taken the top off the trv and pushed the pin up and down just in case it's stuck to no avail. Any ideas what could be the problem? Could there be sludge in the cold kitchen radiator?

Lorian

Could be an airlock. Could just need balancing. Try opening the lock shield valve on the cold radiator just by 1/4 a turn and see if it makes any difference.

Albermarle

If a 1/4 turn of the lock shield valve does not do anything try opening it fully. 

ThisIsWeird

Hi BW.
Clearly only the tiniest trickle is getting through these rads, enough to make one rad luke warm.
The reason one pipe is hot is because it's the 'flow', and there is just enough of this hot flow getting through the rad(s) to make the pipe itself hot - a trickle is enough.
Once this tiny trickle gets into the rad, however, it dissipates its heat very quickly, with the warm rad quickly emitting it into the room. It is therefore returned 'cold' - the second pipe.
If you had a full flow going through, both pipes would be 'hot', albeit with the return being noticeably less so. 
A number of possible causes, so a process of elimination is required.
First - can you confirm that the TRVs are on the 'warm' pipe side?
With the CH running, and the other house rads nicely hot, remove the TRV heads on these two rads to ensure they are fully open. Now turn off a few hot rads in your house - this will force more CH flow towards these two rads. Place your hand on their TRV valve bodies, and see if they heat up. Do they?
Next, as suggested above, pull the caps off the other end's valves, the 'lockshields'. Underneath you should find a metal spindle, with a 'flat' or square at the top that you can grip with a spanner or pliers. 
With the CH still running and the flow pipe still 'hottish', try turning the ls on the 'warm' living room rad anticlockwise (open) a full two or three turns. Place your hand on the TRV valve body, and see if you detect it heating up. 
Please report back.

nofoollikeold

1. Looks to me as if the radiators have been connected in series, rather than in parallel,
2. If this is the case, turning either radiator off will also turn off the other one.  
3. I'd suggest you:
3.1 For each lock shield valve (on the two radiators), close it fully counting the number of 1/8th turns required to close it.  If either or both is already fully closed, you have found the problem.  Then open the lock shield fully.
3.2 For each TRV, remove head, check pin is operating properly, then leave heads off.
3.3 Close the TRVs on all other radiators in the property and see if the problem ones now heat up.
3.4 If they don't you have a blockage in the radiators and / or the pipes.
4. Another possible source of the problem is that the radiators are in drops from above.  Try bleeding the vertical pipes using the drain off points by the lock-shield valves.

FreeBear

nofoollikeold said: 1. Looks to me as if the radiators have been connected in series, rather than in parallel,

Unlikely. As you say, turning one TRV off will turn off both radiators if this were the case. A wider low level shot showing all the pipework under the radiator(s) would help.

ThisIsWeird

Pretty sure it's parallel, as it should be.

boongywoongy

"First - can you confirm that the TRVs are on the 'warm' pipe side?"

No, it isn't. On the dining room side where the radiator is warm, the hot pipe feeds the lock shield end whereas the hot pipe feeds the trv end on the colder kitchen side. 

I switched down the trvs on all the other rads in the house and it did help but it's not terrifically hot (and although the the other rads were switched off, so remained giving warmth but I think that is another problem altogether. 

ThisIsWeird

boongywoongy said:

"First - can you confirm that the TRVs are on the 'warm' pipe side?"

No, it isn't. On the dining room side where the radiator is warm, the hot pipe feeds the lock shield end whereas the hot pipe feeds the trv end on the colder kitchen side. 

I switched down the trvs on all the other rads in the house and it did help but it's not terrifically hot (and although the the other rads were switched off, so remained giving warmth but I think that is another problem altogether. 

The TRV that's fed by the 'cold' - 'return' - pipe, could you have a close look at the chrome valve body and see if there's any pointing arrows embossed in the casing?
When you shut the other rads down, did the properly-cold rad heat up at all?
Don't forget, when you turn a rad down or even off, it'll take a good while to cool fully down.

TripleH

Check the rest of the radiators in the house. Are they all open to their fullest extent?

I was the last radiator in the house before the return to the boiler and my room was always cold because all the other radiators were turned up.

Turn the others (on the radiator thermostat) down low and see if these 2 get warmer.