No heating downstairs

[WtfIgiveup]

Hi. I'm hoping that someone can help me. The other day, I changed a radiator in my dinning room from a horizontal one to a vertical one. Moved some pipes and have no leaks. The only thing is though now, some of my radiators downstairs aren't working, including the new one.
I have a 12 year old Glowworm Micron boiler with a vented system.
At first, nothing worked so I changed the mid position valve and got the hot water and the upstairs radiators and a couple of downstairs radiators working.
Can anyone tell me what I am missing? It's doing my head in now.
Thanks in advance.

Google 'some radiators not working after draining system' There are some sensible-sounding suggestions on the DIYnot forum.

bleed the highest radiators in the house. Does water squirt out forcefully and without dying away?

It does sound like an air lock is possible. As PJ suggested bleed the system carefully. I'm sure you have already checked but:
Have you removed all bungs that you may have used?
Are you sure that when you moved the pipe work you connected to flow and return and not just in one side or other?

One other thought are the tail stocks and trvs too open causing imbalance or alternatively closed?

Hi. I have bled all of the radiators but will try what piglet says when I get home.
I made sure i didn't put the TRV on the wrong side and have tried to balance them.
I was thinking along the lines of an air blockage but damned if I can shift it.
Thanks mini, will have a look later if piglet John's suggestion doesn't work.
Thanks guys, will let you know how I get on later.

I want to know if it squirts out forcefully from the highest radiator in the house.

Did you turn off any valves or tie up the stopcock?

What colour was the water that came out of the old radiator?

I did turn off the other radiators and the water supply to the tank in the attic.
The water that came out of the old radiator was quite clear, apart from the last bit that was black.

Come to think about it John. My highest radiator is a towel rail in the en suite, and I had to regularly bleed it before I changed the radiator downstairs. If I remember correctly, it wasn't very forceful when the water came out either.

I'm interested because, if there is a sediment blockage preventing the system from refilling after changing a radiator, it will be apparent at the highest radiator.

Well, I bled the towel rail and water spouted out straight away with force.
It must be an air blockage somewhere but damned if I know how to get shut of it.

OK

turn off all the radiators except one. Does that one heat up? If so, turn it off and open another. Repeat.

If each of them will work alone, it is probably a balancing problem.

Ok, thanks. I will have to try tomorrow night after work. Been having fun with the pump. Took the big screw out to see if it was sticking, and then it was leaking through the screw. Finally stopped the leak but the kids are in bed now.
I'll let you know how I get on tomorrow.
Thanks again.

there should not be more than a bit of a drip when you take the screw out. If it is a significant leak it might be worn out.

Grundfos pumps are widely used and pretty good, they are a sort of dull brick red. The size is mostly standard so easy to replace, but if you need to, a plumber will cope better with any leaks and floods. Doesn't need a gas engineer. Should last 20 years or more. There are also some cheaper brands.

if you ever do get a plumber in, ask for a system filter which will help prevent future sediment blockages, used in conjunction with a cleaning chemical. This is often needed on an open-vented system like yours, and can save a lot of later trouble and expense.

Thanks for that. It's a Grundfos pump at the moment and there was a lot of water that came out. Looks like I might have found my problem.