Radiators won’t get hot

[NODDYNODSVILLE]

Evening all.
I have open vented C/H system with a heat only boiler and 10 rads over 3 floors.
I have just replaced a rad on the middle floor. Drained system down for new gateway valve for cold feed for header tank. Refilled system no leaks, 👍, but the top top 2 rads won’t get hot.
ALL rads contain water, I have bled all rads. No hot water getting to flow pipe of either rad on top floor.
All other rads are working.
When I bleed the top cold rads, all I get is cold water.
Any ideas or help in helping me would be much appreciated
Simon

 

[NODDYNODSVILLE]

Its strange alright, you have proved that there is water "flowing" to the rads from each individual end so one would think that the pump should circulate water through them especially with all the other rads shut off, I presume these two rads are not on a separately zoned motorised valve.

Only 1 3 way zone Valve
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What size pipework to the radiators?

22mm under floor level, and 15mm from floor to rads in all the system

 

[Ben-gee]

Is it possible that these rads on the top floor are piped up with 2 flows or 2 returns? They would get warm eventually but very very slowly.
I have come across this recently.

 

[king of pipes]

Venting the pump may help ?? with the system running, its definitely is trapped air and if it worked before it should work again no easy way I'm afraid patients and perseverance is the way as the guys have said above and you need a good quality inhibitor in the system . Kop

 

[Ben-gee]

If the system is really that hard to fill and vent one can connect the mains temporarily to the feed pipe from the f&e tank and use a controlled fill to push any air out. Then remove the main feed and reinstate feed to f&e tank.

 

[NODDYNODSVILLE]

Is it possible that these rads on the top floor are piped up with 2 flows or 2 returns? They would get warm eventually but very very slowly.
I have come across this recently.

Morning again, ref Simon Gs post, I’ve just checked the 2 rads that are cold, and the pipe work is 15 mm in the loft and not 22mm. When the loft extension was done about 8 years ago, the builders added these two rads. I thought it was 22mm until the last 150mm going to the rad. But a closer look and it is 15mm. I put the original 8 rads in over 25 yrs ago with 22mm everywhere, apart from going up from the floorboards to the rads for about 150mm. I had noticed that these 2 rads were always slow at getting hot in the past.
I’ve put in Fernox cleaner in at the last refil, and will be using the fernox protector once I’ve got the problem sorted.
Thanks to everyone who’s replied
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Morning again, ref Simon Gs post, I’ve just checked the 2 rads that are cold, and the pipe work is 15 mm in the loft and not 22mm. When the loft extension was done about 8 years ago, the builders added these two rads. I thought it was 22mm until the last 150mm going to the rad. But a closer look and it is 15mm. I put the original 8 rads in over 25 yrs ago with 22mm everywhere, apart from going up from the floorboards to the rads for about 150mm. I had noticed that these 2 rads were always slow at getting hot in the past.
I’ve put in Fernox cleaner in at the last refil, and will be using the fernox protector once I’ve got the problem sorted.
Thanks to everyone who’s replied

I will try and look further for the flow and return pipes to check wher3 they are coming from👍

 

[SimonG]

I've said it before and will say it again.
Turn both valves off to radiators not working. Tray under one side and let water flow out of valve and into tray, decent amount of water as well. Then repeat at opposite end. Same with other radiator.

Had it before on 8mm, 10mm and 15mm pipe.

You say builder fitted loft rads? Plastic pipe?

 

[John.g]

I have got rid of air in one instance by just removing the 1 ins vent blanking plug at one end of the (modern) rad and giving each end a good flush through into a bucket.

 

[SimonG]

I have got rid of air in one instance by just removing the 1 ins vent blanking plug at one end of the (modern) rad and giving each end a good flush through into a bucket.

Done the same with a towel rail.

 

[NODDYNODSVILLE]

I've said it before and will say it again.
Turn both valves off to radiators not working. Tray under one side and let water flow out of valve and into tray, decent amount of water as well. Then repeat at opposite end. Same with other radiator.

Had it before on 8mm, 10mm and 15mm pipe.

You say builder fitted loft rads? Plastic pipe?

All copper as far as I can see.
Will get my buckets and towels ready

 

[John.g]

If your rads are like this you may find it easier to remove the Vent Plug after shutting the valves and first checking that the valves are holding by cracking open the vent then flush through the blank plug end from both sides. But if you think there is some crap in the pipework then the other method my be better.