Upstair radiator fills with air after only 20mins of pump on

18 Jan 2015
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United Kingdom
I recently drained my central heating down to replace the pump.

There were a couple of radiators that I don't think drained down fully because they were below the level of the drain cock but it was enough for me to work on the pump.

System is now back on - I've bled all the radiators (except one as some silly sod has built a cupboard right next to it and I can't fit the key in to bleed it) until water comes out, but after just 20 mins of the pump being one upstairs radiator is full of air.

I've bled all the radiators again starting downstairs but none of them have air in bar the upstairs one.

I've checked the F&E tank in the loft and it has water it in. The pump is on the lowest setting and definitely with the arrow in the same direction as the old one.

The system is (I think) gravity fed HW and pumped CH.

Any suggestions as to what is happening?
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Have a look in your loft.....are there two tanks, one big, one small?
Its the small one you are interested in - check that there's about 3" of water in it. As the system has been drained, its this tank that has to keep it topped up again.
If alls well there, persevere with the radiator bleeding. As the air is evacuated, the loft tank water valve should open to replenish the water so check that's happening too.
John :)

Thanks for taking your time out and replying. Yes got the small tank but I couldn't hear it when refilling. So I'm just draining down again to make sure I haven't got a blockage between this tank and the CH system. The tank has drained and is now refilling. I'm just going to let it runs through for a bit to "flush".

I was bit concerned that I had a bigger problem with the radiator filling with air so quicky?

I've got no leaks on the nuts where I replaced the pump, but I've tightened them again just to be sure.

I'll refill and keep bleeding!
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Please be aware that your inhibitor levels will be very low after this, and should be replenished.
John :)

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