I have oil fired central heating and a couple of upstairs radiators are only heating at the bottom. I have bled all radiators in the house but this hasn’t helped. Has anyone any idea what else it could be?

you haven’t bled them very well…

or heavy water.

If you have a leak, then air will keep entering the system and will find it’s way to the highest point in the CH system…..

If it’s unvented is there pressure in the system as shown on the pressure gage at the boiler?

If its vented is there water in the header tank?

When you bleed does water come out of the bleed port? Is it under pressure?

Are the lockshields on the radiator open sufficiently?

Is the water at the bottom of the radiator really hot or just tepid?

If it’s unvented is there pressure in the system as shown on the pressure gage at the boiler? About 1.5 bar when hot

When you bleed does water come out of the bleed port? Is it under pressure? No water coming out even if bleed valve fully open

Are the lockshields on the radiator open sufficiently? Yes

Is the water at the bottom of the radiator really hot or just tepid? Really hot

Pressure should also be 1.5bar when cold.
Not that that should change the above just a point.

Does air come out when you open the bleed nipple?

Tom only a very small amount of air coming out, not the normal, ‘whoosh’ you would expect

.. ok.. turn off the system let it go cold… vent the ground floor rads and make your way upstairs finishing with the hifghest rad ( normally the bathroom..)
you should get water spurting out of the rad.. or at least running out when venting ( take a tissue or rag) cough..

if not re fill the system to 1.5 bar and start again.. it can take some rads/systems what seems like ages before the water appears..

when each rad is vented.. turn the lot on and be warm..

Thanks all sorted now

a hijack seeing as OP’s is sorted 😀

we have a newish house (10yrs) with original cheapo heating system. I don’t think it’s pressurised/unvented as have header tank etc. of all the radiators (10 plus) one in the kitchen is freezing. If I bleed I get cold water. All others are roasting. could it be the TRV ? or something else ?

When you bleed it does it bleed water under pressure?
Sometimes a TRV might need a tap to release a valve pin at the beginning of a season.

Stoner – thanks, yes, water seems to have similar pressure to the other ones. Might try a gentle tap !

Pressure would not indicate a stuck try as the pressure is the same from the other valve, come on Stoner I expect better of you!
Take off try bread and see if you can move the pin, you may need pliers.

Take off try bread and see if you can move the pin,

better than your spelling big guy! 😉

And anyway – I was referring to two different issues – one pressure, one stuck TRV so thrrrrppppp 😛