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Cool radiators in one room

Discussion in 'Plumbing and Central Heating' started by daveaspy, 6 Jan 2020.

  1. daveaspy

    daveaspy

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    Just moved into a new house and have a problem with two radiators which are only getting luke warm and no where near as hot as the others and really struggling to heat the rooms they are in. I've been under the floor which is quite easy to move around in for the most part and have traced as much of the pipework as I can.

    10CA_floorplan_rads.png

    (I have not yet seen the pipework to rads 11, 12 and 13 as I cannot get under that floor right now - what I can say is that with those rads off, the flow and return pipes still get hot at points A and B - could there be some sort of bypass - they wouldn't just connect flow and return directly with 22mm would they?). There is an upstairs which is working well and tees off near the boiler - I haven't mapped that out yet and am not concerned about it, closing down the upstairs doesn't seem to have any effect on my problem rads.

    Pipework is 22mm for the main flow and return legs as far as I can see, and branches off in 15mm all the way to the rads. What surprised me is the mix of rads that are connected to flow and return (just rads 4 and 8 ) and rads that are connected in parallel with main flow or return pipes(I haven't come across this way of connecting them before). Most rads seem to get hot enough, especially 4 and 8 which get mad hot until I closed them down a bit.

    The problematic ones (unsurprisingly looking at this plan!) are 1 (towel rail in en-suite) and 2 (bedroom rad) - cannot see the exact piping between these rads so assuming a little bit they are like this - I can only see where they tee off the 22mm flow. These two are maybe 4-5m of 15mm pipework away from the 22mm, and the tees on the 22mm are less than half a metre apart - was this ever going to work properly? (surely there isn't enough pressure difference to give a good flow?) The flow is just too low - even with the valves fully open the return pipe of the radiator barely gets warm, the towel rail manages a bit better as its smaller and maybe more free flowing, but still not great.

    So in my mind, the solution is just to repipe one of the legs from the flow over to the return? I'd probably get a man in to do this and its a full drain of the system. Is this the best option?

    In the mean time, is there a configuration of the rest of the rads that could improve the flow through the problematic section? I initially closed down a lot of the lockshields to try and push more water into these rads (expecting everything to be flow/return), but now I've mapped it out I guess this was the wrong thing to do. It looks like the rads in parallel with the flow/return will have very little effect on the flow through other radiators? Whereas opening up rads 4 and 8 should increase the overall flow which might allow more to flow through 1 and 2??
     
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  3. Chris_W

    Chris_W

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    This post doesn’t make much sense to me , sorry. Have you checked if they need bleeding? What system is installed? If it’s a brand new house, why not just get house builder to get plumber back?
     
  4. daveaspy

    daveaspy

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    All radiators bled and system pressure checked - its a worcester greenflow highflow 440 combi boiler. It is only new to me, it is a 1960s build I think.
     
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  5. ericmark

    ericmark

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    You show some radiators plumbed in series and some in parallel, although large buildings like schools had radiators in series most houses have all in parallel, there are a few odd exceptions, fitting a standard radiator in the return of a fan assisted I have seen done, but that is unusual.

    If I have boiler type right, it is a modulating boiler, that is the output varies with the temperature of the return water, it is not just a case of getting hot water to radiators, but ensuring the return water reflects the house temperature, the diagram you show it would be near impossible to balance the system. It may have worked with non modulating boiler, but unlikely to work with a modern one.
     
  6. ericmark

    ericmark

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    In the old school system of radiators in series the water was pumped around fast enough so return was quite hot, under each radiator there was a restriction, but in the main it was thermo syphon that got the hot water in and out of radiator, hot into top and cool out of bottom they did not have both connections to bottom as with modern systems.

    Using fan assisted radiators you would not need the by-pass as the radiator has full flow at all times, the heat output is controlled by the fan speed, however the old system as said often found in schools often radiators at the end of the run were rather cool, I remember in collage the science department said white was a silly colour for radiators, and had their radiators painted mat black, it caused real problems, the science department rooms were really hot, and the rest of collage after that department had very cool radiators, by next year all repainted. The fins in fan assisted radiators are normally mat black.

    Myson radiators are expensive, could the last owners have taken the Myson radiators with them, Myson has both feed and return on one side or at least mine has.
     
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  8. Gasguru

    Gasguru

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    That systems a mess, re-pipe as to a proper 2 pipe system otherwise you'll struggle to balance and get the system efficient.

    Although 1 pipe can work it requires low friction circuits ie. wide bore lockshields/TRVs coupled with tee fittings to help the flow into the radiators.
     
  9. dilalio

    dilalio

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    @daveaspy if that is actually how your system is piped then, yes it's a mess.

    Rads 4 and 8 are getting red hot as they are acting as short circuits on the otherwise 1 pipe system... If you've got the floors up and can access it all, now would be the time to convert it over to a 2-pipe system.
     
  10. daveaspy

    daveaspy

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    ok, so there are no radiators in series - which I understand to mean main flow into a rad, out of rad into next rad, out of rad into next rad etc. They are either between CH flow and return (you might say 2 and 8 are piped in parallel - this is how I thought all radiators were normally piped), or both ends of the radiator connect to the same CH 22mm flow (or return) a short distance apart (I'm calling this "parallel" to the one 22mm pipe). Feels a bit of a mess but as I say it mostly works and looks like it has been like this for quite a long time, the boiler certainly isn't new!

    Interestingly, the radiators connected between flow and return have older style furry material lagging around them, but the main flow/return pipes and the rads connected to just flow (or return) have newer foam insulation.

    I don't have floors up at the moment, but have been crawling through the space under the floor (we are on a hill, so its 4 or 5 feet between the floorboards and the ground underneath in places!) - all the pipework I have seen can quite easily be modified from underneath, just the lounge I would need to access from above (rads 11, 12, 13)
     
  11. dilalio

    dilalio

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  12. ianmcd

    ianmcd

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    I would change to a two pipe system, while one pipe systems can work, mixing one and 2 pipe is not a good idea, sounds like a bigger job than it actually is, you dont need to run 2 new pipes , just a return to the 1 pipe rads and some blanking off or cutting out of tees
     
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