Radiator problem - not heating up

Hebrews12

We have a fairly old radiator which didn't have a TRV (as in it had come off at some stage) and our radiator wasn't getting warm and I assumed it was due to this. I followed a YouTube video and replaced the TRV (see image 1) but it hasn't made any difference.  I notice that the pipe going towards the lock shield valve (the top pipe on image 2) is warm but the rad isn't and then the other pipe also isn't warm suggesting that there might be a problem with the lock shield valve.  I can't get the cap off but I'm assuming it is adjusting it when I turn it.

The really strange thing is that if I have the heating on for a couple of hours, the rad eventually comes on which is a complete mystery to me.  Is anyone able to offer some insight into what might be going on please?  Thanks for reading.  



 

BUFF

I take it that you mean that you replaced the TRV sensor head rather than the actual valve? Did you check to see if the pin in the valve was moving freely?

Hebrews12

BUFF said:

I take it that you mean that you replaced the TRV sensor head rather than the actual valve? Did you check to see if the pin in the valve was moving freely?

I replaced the whole thing.  I kept the old nuts that's all.

Hebrews12

Also, the pipe leading to the TRV isn't warm.

Nobbie1967

Could it be due to sediment in the bottom of the rad blocking the water, but maybe freeing up as it is warmed up. Might be worth removing the radiator and giving it a good blast through with a hosepipe both ways.

Hebrews12

Nobbie1967 said:

Could it be due to sediment in the bottom of the rad blocking the water, but maybe freeing up as it is warmed up. Might be worth removing the radiator and giving it a good blast through with a hosepipe both ways.

OK thanks.  Sounds a little daunting but I'll give it a go.

Ganga

Can you not remove the plastic cap off the lock shield valve to make sure that it is open ,you can force it off with a screwdriver or something heavier ,even if you damage it the metal valve underneath will be ok and new plastic tops can be bought from screwfix ,toolstation etc.

ThisIsWeird

Hebrews12 said:

We have a fairly old radiator which didn't have a TRV (as in it had come off at some stage) and our radiator wasn't getting warm and I assumed it was due to this. I followed a YouTube video and replaced the TRV (see image 1) but it hasn't made any difference.  I notice that the pipe going towards the lock shield valve (the top pipe on image 2) is warm but the rad isn't and then the other pipe also isn't warm suggesting that there might be a problem with the lock shield valve.  I can't get the cap off but I'm assuming it is adjusting it when I turn it.

The really strange thing is that if I have the heating on for a couple of hours, the rad eventually comes on which is a complete mystery to me.  Is anyone able to offer some insight into what might be going on please?  Thanks for reading.  
 
 

Why does it heat up after a good while? Probably just because all the other rads are now hot, so there's spare CH water now getting to this rad.

A boiler pumps out hot CH water, and this will find the path of least resistance. If the water finds that the first rads on the circuit are too far 'open', then it'll go through these, and then return - a bit cooler - to the boiler. The further out, or more closed, rads in the circuit will be missing out on this nice hot flow, and will only get their near-proper flow when these first rads are piping hot, and cannot remove any more heat. That is an 'unbalanced' system.

The solution is to 'balance' the system. This involves tweaking the lockshield valves on all the rads so that they receive roughly the 'same' supply, commensurate to their size and distance from the boiler. So, smaller rads need a more closed-off LS, and closer rads need ditto.

Your naughty rad sounds as though it's either further away from the boiler, has its LS too far closed, or the other rads have theirs too far open.

You've replaced the TRV head - cool, nice job. As others have asked, did you check the valve 'pin' is moving smoothly and freely? If not, it's worth doing as a first step. Remove the head again, and use something solid - a spoon or similar - to help press down the pin. It should require a firm push, but move smoothly, bottom-out firmly ('thunk'), and pop back up instantly when released. Does it? If 'yes', then it's almost certainly ok.

Now turn to the LS - or, in your case, a 'normal' valve. Yours has a 'proper' head on it, one that adjusts the valve. (A lockshield needs its 'loose' cap pulled off, and a spanner used on the spindle underneath). Question - how far 'open' is it? Mark the top of the cap, and then turn it clockwise closed until it stops. How many turns and part-turns did this take?

When this rad finally heats up, how hot is it - as good as the others, of less warm? And, is it hot all over, or slightly cooler towards the bottom (normal), or pretty cool in the bottom-centre (not a good sign...)?

IF your system needs balancing, it might not just be a case of opening up that rad's LS a bit more (tho' that is the first thing to try), but of slightly tweaking closed some other rads that heat up too quickly. In any case, the very first thing to do is to mark all the LSs with bits of tape so that you know how much you move them by; you should always be able to return them to their starting points, in case it all goes pear-shaped...