confusing cold radiator problem! help!

26 Nov 2008
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United Kingdom
I have a very confusing radiator problem!
I have a recently installed (1yr ago) combi boiler in a one-level flat, which appears to be working fine - it heats up 5 out of 7 of the radiators in my flat more than adequately. it doesnt heat 2 radiators though! (the bedrooms- great!)
the 2 radiators it doesnt heat, are the 2 furthest away. confusingly the pipe leading to one of them gets hot (but it takes a while) but the heat never gets past the lockshield valve. the radiator remains completely cold. ive bled it and re-bled it and its got no air locked. i also fully opened both valves- no heat. the lockshield valve appears to be on the flow side (ive guessed this because of the hot pipe - the TRV side is always cold).
so i closed both valves and drained the radiator down, then checked for a blockage at the lockshield side by opening it to see if it re-filled the radiator - it did. so no blockage that end i presumed...
i re-drained the radiator then ONLY opened the TRV which i thought was connected to the return pipe, but the radiator filled up through the TRV!!
what the heck is going on!? the radiator appears to being fed from both sides? is that possible? what might be faulty here? i'm baffled! please help -anyone!
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I doubt you have a blockage. Try shutting down all other rads via the valves and 'forcing' the pump to push water to these rads. modern trv's can be bi directional so it shouldn't matter which side their on. It isalso possible you have an air lock but try the above first and repost
thank you for that - actually i forgot to mention that in the post - i did try that a week or so ago - i shut off all the lockshields on the other rads, but what happened was that when the boiler kicked in and started pumping hot water, the central heating water temperature rose very quickly until it reached its max temperature (about 85 degrees, from memory) and then stopped pumping!
this made me think that the pipe to the cold rad was blocked - but since the pipe right up to it was hot (as in original post) i assumed that i was wrong! very confusing. does that suggest something else at all?
Have these 2 rads ever worked ? Are they minibore from a manifold ?
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Hi yes they have both worked previously - however, one (the furthest away) has never ever got more than lukewarm. the one before it (in terms of distance from boiler), used to be very hot once, even after installation of new boiler...
i forgot to reply to that last bit.. they are both 15mm pipes running to and from each.
where do i look to find the manifold? would it be under the floor?
Close the trv's down on the rads that work (you dont need to mess with the lockshields) then take the trv heads off the other two rads and try pushing and pulling the pins in the centre (make sure the lockshields are fully open) might need a little wd40 on the pins. If this gets them away look in the faq to balance rads properly.
thanks i'll have another go shutting down the other rads when i get home and will post up the results - ive removed TRV heads on both cold radiators previously and the pins do move freely on both.
any idea why i'd be getting water pressure from both sides of radiator? shouldnt the outlet pipe be under negative pressure (suction) or doesnt it work like that?...
thanks all for your help here- the problem is solved!
for info with anyone with a similar problem, i turned off all the TRVs on the hot radiators (rather than the lockshields as i had previously done) and this promoted a bit of hot water flow into the cold rads. i then adjusted the lockshields on the 2 hot rads nearest the cold ones to resrict flow and this worked, meaning the 2 cold radiator became very hot!
so i think the 2 radiators just before the 2 cold ones (in terms of distance) were stealing all the hot water supply because the lockshields were not properly set.
so thanks everyone. im now defrosting!

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