Cold Radiator Help Needed. Any Heating Experts In?

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  • Cold Radiator Help Needed. Any Heating Experts In?
  • andysredmini

    Hi all.
    After moving house a few months ago I have finally got round to trying to sort out a cold radiator problem.

    It’s a traditional central heating system with a boiler, hot water cylinder, 2 feed tanks in the loft and a motorised valve. Most of the radiators including the cold one are being fed by 10mm copper pipe.

    Things I have tried so far are
    •Bled system including every radiator and the air vents by the cylinder
    •Turned every other radiator off except the cold one. This made no difference.
    •Remove radiator and flush
    •Drained down entire system and filled back up x2
    •Drained down and filled back up adding sentinel cleaner. Left this in the system for 4 weeks.
    •Replace TRV on right hand side with a new non TRV (I couldn’t get a TRV to fit the old size thread)
    •Checked left hand valve (opened and hot water came out under pressure)
    •Whilst the radiator was off I flushed it again. Whilst flushing I blocked the other end to make sure water was coming from the bleed screw hole.

    Whilst the radiator was off I tested the valves again and the left one when opened shot hot water out under pressure but the right valve just trickled hot water out (which I assumed may be correct as I wouldn’t expect pressure on both sides of the radiator).

    When the radiator is connected and the system is running the valve on the left (the one that shoots out hot water under pressure) is cold but the right (the one that dribbles out) is hot.

    Any help would be great as I’m out of ideas. I would rather try and fix this myself if possible but I guess I’ll get the answer of needing a power flush. I would rather avoid this at the moment as I want to get a new boiler before next winter and would update all the TRV’S and get it flushed out at the same time.

    Many Thanks



    Surely the one pumping the water out should be hot as that’s the flow side?
    Only thing I could think of would be a blockage in the return pipe off the main runs therefore stopping the hot water circulating?


    That’s all I think that it could be.
    How would I clear a blockage without specialist equipment?
    I have a plumbing pressure gauge with a bike pump valve that connects to a 15mm copper pipe. Could I connect this up and try and blow it out?



    Premier Icon mtbfix

    I had a powerflush done earlier this month on a recommendation. It did not fix the one cold rad. Unless its a massive or fancy job it might be just as easy to get a new rad and have done seeing as you’ve tried pretty much all other avenues.


    Are you sure the rad valve ( if its a thermostatic one ) is actually opening? I’ve had a few where the operating pin sticks, especially on rads that are not switched on often.

    Premier Icon midlifecrashes

    Don’t try to blow or force the blockage. If you can get at the pipes to feel where the blockage is, cut it out and replace the section, or cut into it further upstream and blow it out backwards.

    Premier Icon footflaps

    How would I clear a blockage without specialist equipment?

    You can try filling with something quite viscous like Fernox DS-40, although check your boiler heat exchanger is compatible.

    Failing that, I’d try feeding some wire down the pipe to see if you can locate the blockage, it can’t be that far away unless your radiators are massively spaced apart (stately home)?


    I wasn’t sure the existing TRV was opening/working properly and the pin looked slightly bent so I planned on removing it and taking it to a plumbers merchant to get a replacement. It was corroded and had been painted so I had to cut it off the pipework only to find that a replacement wasn’t available due to it being an old size. I ended up replacing it (temporarily) with a normal valve.


    I have no chance of getting to the pipework as it appears to come out of the wall with no indication of what direction it is going in.

    Wire sounds like a good idea. We have rolls of 4mm at work I can probably borrow a bit of. Is it as simple as feed/twist it in and hope?
    Knowing my luck ill probably just hit a t-junction!

    Annoyingly I was sure it was going to be the valve I put in some new inhibitor which will now just end up down the drain. Or is it feasible to capture it and re use it? it only went in on Saturday.


    I would expect water to gush from both the flow and return with equal force; the pressure is the same after all.

    The wire down the pipe seems the best solution to me though I’d be a little wary of dislodging something like a lump of solder and sending it into the pump impeller. Can you send the wire down with the pipe full of water in the hope that the pressure might flush out the obstruction? Failing that, cut out the section between the rad and the main pipework and replace.

    Yes, I would try to save the inhibitor and reuse it, as long as the water is generally clean.


    I you shove a wire down to dislodge the obstruction make sure you’ve got a plan should it work! Hot water in the face rarely brings a smile.


    How do you plan to save the inhibitor……. Bearing in mind you will have to store the whole volume of your heating system and get it back in some how.

    Is the wAter coming our the rad and the bleed valve when you flush clear or black ?

    Premier Icon Nobeerinthefridge

    I had the same issue, there was a copper pipe kinked below the floorboards.

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