One radiator won't heat up at all

Discussion in 'Plumbers' Talk' started by DIYenthusiast, Jan 10, 2020.

  1. DIYenthusiast

    DIYenthusiast New Member

    When you top up normally, how do you tell its been refilled adequately. Do you rely on the pressure dial alone? How long do you keep the first one open before opening the second. I usually follow one after another, unless the screwdriver head takes time to locate correctly.
  2. Hans_25

    Hans_25 Screwfix Select

    You fill the system until you have 1.5 bar or so, then bleed each rad and boiler vent (if needed) and put more water in to top up the pressure. As you bleed the rads you'll find less water is needed to top up the pressure as there is less air in the system and air compresses whereas water does not. I find its handy to have the OH operating the filling loop as I bleed the rads, just tell her to keep the pressure to around 1.5 bar or so.

    Re the two valves, as I mentioned above these are in series. So open one and nothing will happen. Open the second to top up as required, then close both off once you're finished.
  3. DIYenthusiast

    DIYenthusiast New Member

    It's the other way around (might have been all along) it is the lockshield that passes water but the TRV side doesn't. Also, there is a very quick (1 second) sound of water/air trying to pass into the radiator (or at least it sounds like that) as I am reopening the TRV from closed to open. This only happens after I've bled with lockshield open/TRV closed, but not any other time when I rotate the TRV head.

    Faulty TRV a possibility? If so, I assume the whole TRV requires changing and not just the head.
  4. Hans_25

    Hans_25 Screwfix Select

    The TRV body is likely stuck in the closed position, so its either unsticking it, or replacing.
  5. terrymac

    terrymac Screwfix Select

    Fit a complete new TRV.
  6. DIYenthusiast

    DIYenthusiast New Member

    It's not stuck. That's one of the first things I checked a few weeks back when I started trying to resolve the issue. Wish it was as it would have been so simple.

    I guess I'll have go to over to B&Q and get a new TRV.

    Thanks everyone who helped out in the thread.
  7. DIYenthusiast

    DIYenthusiast New Member

    I've not swapped it yet. I just watched another video in which the guy said draining the system down can sometimes lead to air trapped in the pump. I've not had this issue on ocassions I've drained previously, but I don't want to open the boiler up and do anything in there. Someone earlier mentioned there shouldn't be trapped air in a pressurised system but I have had to allow air out in one or two radiators to get them to work highly efficiently, especially after draining when one radiator seemed to be full of air (which I let out with a bleed key).

    In those videos, they also mention shutting the main water source. I never do that when I drain. I assumed since the refill valves were closed more water wouldn't enter the central heating system anyway (unless I refill myself)

    Usually what I do when I drain the system:

    1) off the electric switch to the boiler

    1) use the drain cock on the lowest point radiator

    2) keep all the rad valves (TRV and lockshield) open for each rad

    Am I taking the right steps, or is something else required?

    By the way, is there anyway to isolate Nd drain just the radiator I will be working on other than freezing the pipes (which I am not going to do).
  8. Hans_25

    Hans_25 Screwfix Select

    If you close both valves on a radiator it will remain full, so can do that if its easy to do, but the flow and return pipes will still drain down. Just be careful if you have things like a Magnaclean as they can act as an air lock and if not vented, you can suddenly get a massive glug of water coming out hours after you've drained down! Same goes for the boiler itself if its situated high up (as mine is, on the first floor).

    When I drain down I like to do so fully and properly as its normally because I want to solder some fittings and you want to be 100% sure there's no water present. If its just compression fittings being worked on, not so important.
  9. terrymac

    terrymac Screwfix Select

    An air lock ,and air collecting at the top of a radiator are two completely different things.
    Yes ,you can drain one radiator to work on or remove the radiator. But if you are going to remove a valve it's better to drain the system down. It is possible to swap a valve without draining down , but I wouldn't suggest that you try to do it that way.
    Is your boiler a combi boiler ?
  10. DIYenthusiast

    DIYenthusiast New Member

    Tried to replace the TRV but after loosening the nuts the TRV wouldn't pop out. I've seen videos where the TRV comes out very easily once the nuts have been fully loosened. Is my thread (I think is what is called) too long that it goes too far into the pipe/valve that goes connects the TRV to the radiator side? Aren't they all a standard size. My TRV is Giacomini.

    I don't want to really undo the lockshield side and get the radiator off the wall.

    By the way, despite draining the system I found when I loosen the nut on the TRV that connects to the vertical pipe (the flow), water is still streaming out. Is this something to do with the possibility that the faulty TRV blocking the water coming into the radiator was now opened hence the water still coming out. It was easily controlled as I only needed to tighten the nut to stop it. The other side was merely trickling from the remaining contents from the radiator itself.
  11. terrymac

    terrymac Screwfix Select

    Can you post pics of your radiators valves ,both sides of rad ,and the new TRV ?
    I don't follow what you describe.
    Depending on EXACTLY how you have " drained " the system ,the rad in question ( and the two pipes going to it) may well still be full of water.
  12. Hans_25

    Hans_25 Screwfix Select

    I made some changes to my CH system pipework, refilled it, found a leak then drained. Tried disconnecting the HW cylinder pipework and water kept on coming out. Then realized I'd reconnected the bit of pipework to above first floor level so there was an 18" head of water above where I was working!!

    Drained down from another downstairs radiator and all good :oops:
  13. DIYenthusiast

    DIYenthusiast New Member

    Current TRV

    New TRV

    By the way, can I replace the existing TRV with a standard valve, as opposed to a new TRV, with something like below. We leave the room at max all the time anyway. Our heating either goes for certain length of time or we control it via the room thermostat. I am guessing these type of valves never really go faulty.
  14. terrymac

    terrymac Screwfix Select

    Both existing TRV ,and the new one look to be a straight forward like for like swap. I don't know what difficulty you are having ?
    Can you remove the TRV from supply pipe and the union of the tail ?
    Are you leaving the two nuts in situ and trying to connect the new TRV to them ,but the nuts are not screwing onto the TRV' s threads ?
  15. DIYenthusiast

    DIYenthusiast New Member

    When I loosen the nuts the existing TRV doesn't come out of the radiator or lift out of the supply pipe. It lifts out of the the supply pipe a little but doesn't come out fully.there is still a little bit of the TRV that remains in the supply pipe. I can't move the supply pipe back a little to create room to slot the TRV out of the radiator as it is very firmly in place. To be fair, I didn't really struggle too much as I didn't want to risk damaging the supply pipe.

    I loosened both nuts completely and moved each to the side as far as they would go. It's not the nuts that are stoooppinh then TRV from coming out. Maybe the thread of the TRV is too far into the radiator.
  16. terrymac

    terrymac Screwfix Select

    The pipe goes into the bottom of the valve around 10 mm (ish). And the same at the other union. So you do need to pull it out , which will put a bit of strain on the pipe if it is rigid.
  17. Hans_25

    Hans_25 Screwfix Select

    Could try lifting the rad a bit...or pull the TRV to one side having undone the union that attaches TRV to radiator first.
  18. DIYenthusiast

    DIYenthusiast New Member

    I could do. Lifting the rad might free it up. But I now have a fair idea why it didn't pop out last time.

    I am going to fit the TRV in a couple of days or so, just going to let the current cold spell subside a bit first.

    I have two further questions.

    Can I leave the water in one radiator in when draining by closing the two valves (TRV and lockshield). Or does the entire system need draining? For some reason this radiator doesn't fill up the first time when I refill (happened twice). This along with two other radiators didn't work right away after refilling the system. The three are sort of in line, consecutively. Both times it was the three same radiators. I had to drop some pressure by bleeding them (especially the bigger one in the hallway downstairs) and top up to get them going on both ocassions. DO I NEED TO OPEN THE BLEED VALVES OF ALL THE RADS WHEN DRAINING?

    Secondly, do I need PTFE around the threads of the new valve?
  19. Hans_25

    Hans_25 Screwfix Select

    Yes, as long as its not the radiator you're working on. Will still need to be bled afterwards though.

    If you want to drain the water out of the rad then yes, otherwise the rad is an air lock and the water will hold there until.....glug whoosh.

    If you're screwing a new valve bit into the rad then yes. Normally 15 turns will do, sometimes 25, in the correct direction so it doesn't unwind as you screw the thing in. It wants to be a tight fit! Look at YouTube.
  20. DIYenthusiast

    DIYenthusiast New Member


    Actually, I find it is the lockshield side that doesn't bleed. The TRV when open does bleed.

    But I did manage to get both the flow pipe and the lockshield warm when I undid the nuts on the TRV the other day and the water started flowing out of the flow pipe into a bucket. This is the first time the lockshield warmed up since the radiator stopped working, whenever that was. But when I closed the nuts,the pipes started cooling down again.

    Does this mean the lockshield valve is faulty, or there is a possible block in the pipe leading up to this radiator, in which case I'll need to call in a plumber.

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