Cold downstairs radiators, luke warm upstairs. Any ideas??

27 Jan 2008
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United Kingdom
Initially I thought it was the pump that was working. So I put in a new one, now it seems that the pump is trying to pump but can't. The pump is making a loud humming noise.

The radiators upstairs are lukewarm (presumably by gravity-feed rather than by pump), hot water is fine but all the downstairs radiators are cold.

I have bleed all the radiators and on some of them, nothing comes out which suggests that the pump is not pumping.

Any ideas as to what could be causing this
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If no water is coming out of the rads they are either not full or you are airlocked.......
you need to add more info or re write this info as it makes no sense.

i thought it was the pump working. when ?
pump is trying to pump. when is the heating called for or hw called for what ?
i have bled the rads but no water comes out, suggests pump is not pumping.

water should come out if pump running or not.
How do I get rid of an airlock? Someone has suggested draining the whole system down and flushing all the radiators with a hosepipe. Is that right?
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its an airlock not a blockage.
if its a certain rads not getting hot shut the hot rads open the cold fully and turn the pump speed up soon shift it.
So I need to shut all the radiators upstairs and make sure that all the radiators downstairs are open (which I'm sure they are already)? Is that right?
yes if you shut all the flow side down on the working rads then you won't disturb the locksheilds if the systems balanced.

leave down stairs open.
you should feel the heat coming down the drop down pipework downstairs.
stick the pump on full speed and hw calling off on the programmer just heating on.
[ if you shut all the flow side down on the non working rads] Sorry? It is the downstairs rads that are not working but surely you want them open. Do you mean shut the flow side down on the working ones, which are upstairs?
yes sorry upstairs working rads close downstairs non working open.
pump on full
I did all that and it didn't work. In the end, I drained the whole system down to discover there was a blockage in the pipe from the header tank to the pump. The pipe was full of silt (probably from the header tank itself).

Although all the radiators are now hot, the pump seems to be making an excessive humming noise, as if it is overworking. Also, the pipe from the header tank to the pump is getting hot. Is it suppose to get hot?

Do you think it is an airlock which may sort itself out or do you think silt has got into the system and there is a small blockage somewhere in the system making the pump work excessively?
Ok you have a blockage not an air lock. The cold feed is blocked. Drain the system, bung the cold feed at the tank end. Where the cold feed joins the system, cut it about 70mm up (then you can put a compression fitting back on) rod it through with a long thin screwdriver. once done refill the system.

To clear air locks you will need to turn the pump speed up and down and hold it between speeds to stop it. Doing this will send bursts of water around the system. Whilst holding it between speeds, the pump stops, keep it held until you hear the air bubling up the open vent.

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