Problems with new radiator

Discussion in 'Plumbers' Talk' started by i_nod, Jan 15, 2008.

  1. i_nod

    i_nod New Member

    I've just replaced an existing (traditional style) radiator with a tall classic column radiator. However the new radiator isn't heating up, I can feel heat coming into the inlet pipe but the bottom of the radiator is never more than luke warm and the top is stone cold - it's as if there is no flow (or limited) flow through the radiator.

    The central heating system is a one pipe system rather than the traditional two pipes for flow and return i.e. both radiator connections connect into the same pipe. The single pipe is 15mm copper. The old radiator use to heat up fine and would have been of a similar overall volume to the new radiator, so the only difference is in the style of the radiator (its very tall), and location - the new radiator is located slightly further along the wall than the old radiator.

    I had to extend the pipe run slightly to accomodate the new position, and one side of the radiator has a few kinks in it to accomodate around a joist. I've never got the hang of bending pipes, so all the kinks are created with soldered 90 degree elbows.

    The radiator instructions said to position radiator such that the water flowed in through the opposite side to the air vent. Its possible I've got this wrong as I wasn't able to work out the direction of flow through the pipe.

    I'm using drayton thermostatic valves on the raditor, however these are both currently wide open while I get it working.

    So my questions are really around how I trouble shoot this. I'm really at a bit of a loss here, but my thoughts are:

    1. Could I have installed the radiator the wrong way round? Why would the direction of flow be important (the radiator filled up with water ok)?

    2. Could the four elbows I had to install in one of the inlet pipes be restricting the flow?

    3. I know a single pipe system is far from ideal, however the old radiator use to heat up fine. Could the new radiator just not be suited to a single pipe system?

    Any advice much appreciated...


  2. HOTDOG ø

    HOTDOG ø Active Member

    Most vertical rads have flow tubes or devices inside to ensure the water circulates properly.

    TRV's on a one pipe system are not always a success.

    The biggest failing of a one pipe system is getting the water to go thru the rads and balancing the system - as you are discovering.
  3. i_nod

    i_nod New Member

    So from what you said, reversing the rad would possibly make a difference?

    On the TRV side - the TRV is fully open i.e. it doesn't have the operating head fitted yet. I know the TRV has a smaller bore than a standard valve. Is this likely to cause an issue?

    BTW, the old rad just had standard valve's on it that were always fully open.

  4. devil's advocate

    devil's advocate New Member

    Hi i nod.

    I think you understand the problem! :(

    Good chance the old valves were also designed for a one-pipe system - they could very well have wider bores. Check your local Plumbers' Merchants and see if they have valves for a one-pipe system.

    I don't think it matters too much which way round your rad is fitted. Bleed it with the pump switched off. (I think their spiel was to do with the possibility of the bleed screw drawing in air if opened with the pump running and the pipes connected the 'wrong' way round.)

    Because of the nature of the one-pipe system, the water really couldn't be arsed going through the rad unless the path is made smooth for it - so any kinks, extra lengths of pipe etc certainly won't help.

    I, too, have a one-pipe system :)(), but it works pretty well :))), even with a new condensing combi. One rad is even fitted to the other side of a wall to where the pipes are running, so quite a few elbows there. Heats up ok, tho'.

    So, unkink your kinks you kinky thing, and try and get wide-bore valves. Perhaps forget fitting the TRV unless you can get a wide-bore one of them too.
  5. Bungditin.

    Bungditin. New Member

    If you look through the rad where the valves are connected and you can see right through,this end goes at the top and if you can't see right through that's because there's a baffle which sends the water up the radiator that end goes at the bottom.
  6. Captain Leaky

    Captain Leaky New Member

    Good flow is critical on one pipe, get rid of the TRV, check rad is clear, any spreaders or flow tubes? and balance the system.
  7. i_nod

    i_nod New Member

    Thanks for the advice,

    So from what people are saying:

    1. Try removing the TRV's.

    2. Look through the radiator. If there are baffles try turning it (its not upside down - just back to front).

    3. Try straightening the pipe run as much as possible. Not sure how possible this is as the inlet is above a joist so has an S kink in it. I might be able to put a couple of 45 degree bends in rather than the 90 degree elbows.

    Anything else worth checking? I guess I could always try shutting the other valves on the circuit to see whether that has any effect (which I guess is part way to trying to balance the system)?

  8. i_nod

    i_nod New Member

    I guess the only thing that I'd add to the TRV theory is that I've replaced/moved pretty much every other radiator in the house adding TRV's to each in the process. I've not had any problems upto now, however I'll try removing them and see what difference it makes.

  9. Bungditin.

    Bungditin. New Member

    when you remove the valves look through the rad like i said,customer had the same trouble recently,spent most of the day trying to improve the heating when it was found out the rad was upside down.
  10. i_nod

    i_nod New Member

    The Rad can only go one way up - the top has one position for the air vent and the other side blanked off. At the bottom of the radiator it has openings either side for the inlet and outlet. So the radiator can only go in one vertical orientation.

    The instructions say to ensure connection flow enters through the opposite side to the air vent - but don't say why. So it can go in two possible horizontal orientations.

  11. Captain Leaky

    Captain Leaky New Member

    Then connect it the way they say, there will be baffles inside which you may not be able to see, if you have connected the flow to the other side that may well be why you are having problems.

    Vertical rads are always more fussy than horizontal.
  12. Bungditin.

    Bungditin. New Member

    The one i fitted had top and bottom stickers on it but the suppliers had put them on the wrong way around,so don't always go by the instuctions,best to make sure first than having to drain it down and remove.
  13. ­

    ­ New Member

    The radiator instructions said to position radiator
    such that the water flowed in through the opposite
    side to the air vent. Its possible I've got this
    wrong as I wasn't able to work out the direction of
    flow through the pipe.

    1. Could I have installed the radiator the wrong way
    round? Why would the direction of flow be important
    (the radiator filled up with water ok)?

    If the new rad has a flow riser tube or baffles and you fitted the rad the wrong way round then this is most likely your problem. That's why the instructions said to fit it a particular way round. If it didn't matter which way round it went they wouldn't have mentioned it.

    I've worked with one pipe systems where gate valves have been installed on the 'one pipe' between each pair of rad valves. This has given the chance of restricting the flow through the one-pipe and forcing it up into the rad. Not ideal but on large extended one pipe systems this can sometimes be the only workable option.

    I assume you extended the 'one-pipe' right up to and under the new rad and you didn't just extend the rad tails? If you did just extend the rad tails then the water will take the route of least resistance and miss out the rad altogether.
  14. plummit

    plummit New Member

    Sorry for sounding thick,
    But there must be a fundermental problem, as hot water always wants to rise.
    I cant invisage a single point entry/ return on the rad with a one pipe system. Sorry for being so thick, but pictures would help me !.
    Old one piped system had the feed to the top of the rad, possibly fed via swept Tees, and the return at the opposite side on the bottom.
    I could imaging getting upset that the rad did not work, then cutting it in to the flow/ return. But having no control over it.
  15. i_nod

    i_nod New Member

    ecm - I did extend the one-pipe loop rather than the tails. However, one of the tails is slightly longer than the other due to an awkwardly positioned joist so it does have slightly further to go (no more than 0.5m) with a couple of extra elbows in it to get it in the right position.

    I have put a couple of calls in to the rad manufacturer to determine whether direction is important, but so far they haven't returned my calls <sigh>. From all the feedback I'm getting, this sounds like the most plausible reason, so I'll have a go tomorrow night at turning it round (hopefully the rad manufacturer will return my calls and confirm it).

  16. i_nod

    i_nod New Member

    plummit - Not completely sure of the mechanics myself, but I have a single pipe running around the house. The radiators are standard rads with the inlets at the bottom and are both connected into this pipe. You can visualize it as a single pipe running horizontally beneath the raditor which both inlet are tee'd into.

    It does work - the whole house is plumbed onto this single pipe. It does seem to take a while for the radiators to become warm - much longer than my previous house - but that could equally be caused by the single pipe being 15mm.

  17. Cobblers

    Cobblers New Member

    ;-D Make sure you havent blocked the rad valve(s) with PTFE
  18. plummit

    plummit New Member

    One piped systems, can never be as effective as a two piped system. I have worked on a few single feed systems. And wonder why they are actually there,
    I appreciate that in huge properties, you work with what is there. You can pending the rad, incorporate it into the "flow and return" loop. It will work !!, but you would have no control over the rad, as it has become part of the loop. IE shutting it down would shut down the system basically.
    One piped systems went out probably before primatic cylinders died a death.
    Yes they will work, but to what degree.
  19. devil's advocate

    devil's advocate New Member

    Hi Don.

    Just to sum up much of what's been covered already.

    Yes, one-pipe systems do work - as you've discovered they just take longer to get up to speed! I've also fitted TRVs to my standard rads on a 1-p system, and they work fine.

    I also have a rad which is on the other side of the wall from the 'system loop' - for the tails to get to this rad there are at least a couple of elbows on each end, and an extra half-metre or so of pipe at one end. The rad still heats up perfectly well.

    Yes water will take the path of least resistance but, like electricity, some will always take the 'high' resistance path too, unless this resistance is waaaay too high!

    So, I suspect your rad would heat up ok if it was a 'normal' type regardless of the extra pipe/fittings involved. Clearly this vertical rad is either fitted incorrectly or is just a tad more 'sensitive' to such situations (you can well imagine that it would contain baffles to force the water to circulate fully throughout, and these baffles would place extra resistance on a normal 2-piped sysatem - and could well be the death-knell on a one-pipe type - its resistance is just too high).

    So, after finding out about the rad itself, if there's any mileage in continuing with it, it'll be a case of reducing anything that's causing friction to the flow.
  20. i_nod

    i_nod New Member

    Eventually got the radiator working. The problem I guess is that this radiator is just not well suited to a one pipe system, so I've ended up installing a gate valve in the one pipe between the two tails. This is now half closed and the radiator is heating up fine (TRV's also removed).

    Only downside is that the downstairs radiators now heat up slower than upstairs which I guess is down to the increased resistance in the downstairs leg.

    Anybody see any problems with leaving the gate valve perminently in place?

    BTW, the direction of the radiator does matter. There's a baffle on the inlet which sends the water straight up the first column such that it then finds it way down the remaining columns to the outlet.

    Thanks for everybodies help,


Share This Page