Not the normal sticky TRV Cold radiator problem

[CarlBrown]

Hello all,
First of all, people on here seem to know what they're talking about. I've been through all the FAQs and common problems pages, plus trawled through lots of forum posts where people are having similar problems as me, but so far they've all been fixed by simply tapping the TRV pin. This hasn't worked for me! So i thought i'd finally post and see if someone can help me out.

We bought a 2nd floor flat in the summer, recently turned on heating and one radiator (master bedroom) is stone cold, and both pipes leading into it were cold too. Apparently boiler has been regularly serviced for many years. and i think it's probably the furthest rad from the boiler.

It's a 2 pipe system and all radiators have TRVs fitted to one end and at the other is the normal control flow valve (not a lock shield, which i'm slightly confused by too? i thought the TRVs were supposed to be replacements for the flow valve not the LS valve? unless they've all got the wrong cap on and are actually LS valves?)

Now, i've tried hitting the pin and nothing happened (Have had success with this method in the past on a different rad however). Read lots of posts, saw a few suggesting turning all other rads off and leaving the cold on one, then jack up the pressure and see what happens. Did this, pressure at 2 bar (poss a bit high?) left it running on max heat for 15 mins and finally the pipe leading to the TRV started getting hot. Joy i thought, but then nothing more. That end of the rad started to get lukewarm at best, but i put this town to heat transfer through the metal as nothing more happened.

Have bled all radiators now, no air anywhere.

The odd bit, that i'm sure someone here will be able to help with, is this: I cracked the nut joining the TRV to the radiator, hot water came out for 2 seconds, then stone cold (presuming it just drained the water that had heated through transfer, then that left only the cold water in the rad to come out) so i thought, it must the TRV is stuffed. I'll get t a new one.

Then i read another post on here from someone saying crack the other end and see what happens, it might not be the TRV. So i did.
When i opened the nut at the other end (control flow valve NOT TRV) suddenly hot water came flowing out and the other pipe going into the ground got hot. Until i tightened the nut up again, then the heat slowly dissipated leaving me feel very disappointed!

So i'm totally confused. The pin in the TRV moves freely, so is the valve itself knackered?
The control flow valve moves freely, but maybe that valve is knackered?

Or might there be an airlock somewhere else?

Or am i describing the symptoms of a rad filled with sludge that needs draining and flushing?

Any help would be very much appreciated as it is getting cold in there and it's only going to get worse!

Carl.

 

[Steve69the69Gas]

Hi Carl + welcome,

I would now isolate this rad, drain it, flush it out and check the valves open and let water out. But be careful most TRVs will still pass water when screwed down, so use the decorators cap method and take the trv head off and screw down decc cap.
Hth

 

[Registered Gas Man]

Airlock possibly.

Any drain point on rad?

If so attach hose pipe open drain point and leave filling loop/point open for 30s or so.

Turn off drain point, close filling loop. Job done hopefully.

Beware: Try not to over fill the system.

 

[D_Hailsham]

It's a 2 pipe system and all radiators have TRVs fitted to one end and at the other is the normal control flow valve (not a lock shield, which i'm slightly confused by too? i thought the TRVs were supposed to be replacements for the flow valve not the LS valve? unless they've all got the wrong cap on and are actually LS valves?)

A LS valve is nothing more than a control valve with a different top! At least you will find balancing easier; but you should really change the caps to prevent anyone fiddling with them.

Are your TRVs bi-directional? (They will have two arrows at right angles on the chrome body). If they have only one arrow, this must point in the direction of flow - towards rad on flow, away from rad on return. If they are bidirectional, they can go on either end and any orientation.

It's just tradition that the control/TRV goes on the flow and LS on return, they will still act as expected.

 

[CarlBrown]

Thanks for the help so far gents!

No drain point on rads, so will have to take it off the wall. Probably for the best anyway....

Thanks for the info on the LSV....i've often wondered if this was the case but since they were so regularly referred to by different names, i just assumed they were different!

Off to the shop to get a decorators cap.

Do i just close of both valves at either end, loosen bolts then lift rad off wall to flush etc?
I don't need to drain the entire system to flush this one rad, right?

Thanks, Carl.

 

[kevplumb]

Do i just close of both valves at either end, loosen bolts then lift rad off wall to flush etc?

gonna make a mess if you do

close valves

have a tray or similar handy and a bucket

undo one end union and drain rad into tray

empty tray into bucket

 

[bengasman]

...but so far they've all been fixed by simply tapping the TRV pin.

That probably means your system is corroded, or you have poor quality trv's

Apparently boiler has been regularly serviced for many years.

What makes you think that?

It's a 2 pipe system and all radiators have TRVs fitted to one end and at the other is the normal control flow valve (not a lock shield, which i'm slightly confused by too?

Lockshields and wheelhead valves are essentially the same. The fact that the "installer" stuck wheels on them instead of caps, means he didn't have a clue.

The pin in the TRV moves freely, so is the valve itself knackered?
The control flow valve moves freely, but maybe that valve is knackered?

Probably

Or might there be an airlock somewhere else?

Unlikely but possible

Or am i describing the symptoms of a rad filled with sludge that needs draining and flushing?

No. That does not mean your system is clean though, it is just not an indication of it

 

[CarlBrown]

Apparently boiler has been regularly serviced for many years.

What makes you think that?

- The previous owners told me so! Plus, the two radiators that have given me trouble both have fairly new looking TRVs with British Gas plastered all over them (all the others work fine although are very old looking). So i suspect previous owners had boiler and pipes insured with BG, found one winter that radiators in master bedroom and second bedroom didn't work, called out an engineer who replaced valves......then i move in and problem is still there! perhaps this means it isn't the valves....

Lockshields and wheelhead valves are essentially the same. The fact that the "installer" stuck wheels on them instead of caps, means he didn't have a clue.

Oh dear. i can only hope that previous owners bought a job lot of replacement valve covers rather than it being the installer!

Thanks everyone that's posted so far....I have a 1 year old so i'm having to do the work when he's not trying to sleep. (Fortunately his room is nice and warm though.) but i do appreciate all your help and i'll let you know how i get on.

Carl.