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

 

[ShaunCorbs]

Try turning all of the others off then running the heating should move any air around and they should get warm

 

[NODDYNODSVILLE]

Try turning all of the others off then running the heating should move any air around and they should get warm

Thanks, will try that.

 

[Aquarius]

You did use the flow and return? I’ve seen one where both sides were piped up to flow.

 

[NODDYNODSVILLE]

You did use the flow and return? I’ve seen one where both sides were piped up to flow.

Morning, the pipe work for the 2 rads at the top of the house, which stay cold, has not been changed.
The rad I changed, used the original pipe work and got hot.
After I changed the rad, I refilled the system, checked for leaks, bled each rad starting on ground floor and furthest one from boiler. Repeated this on 2nd and 3rd floor, water coming out of all 10 rads. Fired the boiler up, only 8 rads get hot.
Rather confused. Thanks for replies.

 

[SimonG]

Air locked. As Shaun said above. Shut everything else down. Failing that disconnect flow and return and let them flow into a bucket.

 

[NODDYNODSVILLE]

Thanks, will try that.

E
Evening, tried turning TRVs off of the other 8 rads, still no joy. When I opened the TRV on some of the rads, there was a gurgling, bubbling sound. Would that mean there is air in the system.

 

[John.g]

When you say 2 rads at the top of the house, are these 2 rads on their own in/on the third floor, if so check that the F&E tank if installed is full or if not that the system is pressurised when cold to 1.0 bar, you may not have enough static head.
Edit: I see you have cold water and a header tank so static head shouldn't be a problem, with circ pump on when you run the two rads on their own check that that they are still venting and not drawing in air, I have a rad in my attic bedroom that never vents water while running but does heat up.

 

[SJB060685]

E
Evening, tried turning TRVs off of the other 8 rads, still no joy. When I opened the TRV on some of the rads, there was a gurgling, bubbling sound. Would that mean there is air in the system.

That suggests either air yes or the system isn't completely filled.

 

[John.g]

Should also add to check water venting (circ pump off) from each rad with flow valve shut only then return valve shut only and repeat this with circ pump running.

 

[NODDYNODSVILLE]

Air locked. As Shaun said above. Shut everything else down. Failing that disconnect flow and return and let them flow into a bucket.

Do you have to shut both valves on all the working rads. Because I tried shutting TRVs and leaving lockshieds open on working rads and still did not work.

 

[SimonG]

Just TRVs. Shut all bar 1 of the 2 not working. Possibly a rad or towel rail with 2 manual valves?

 

[NODDYNODSVILLE]

When you say 2 rads at the top of the house, are these 2 rads on their own in/on the third floor, if so check that the F&E tank if installed is full or if not that the system is pressurised when cold to 1.0 bar, you may not have enough static head.
Edit: I see you have cold water and a header tank so static head shouldn't be a problem, with circ pump on when you run the two rads on their own check that that they are still venting and not drawing in air, I have a rad in my attic bedroom that never vents water while running but does heat up.

Do I need to close both valves on the working rads, then start the heating, as yesterday, I only closed the TRV
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Would opening up the drain on the bottom lowest rad clear the air lock, when the header tank refills.
All rads have water in, no more air coming out. The 2 rads are in separate bedrooms on the top floor loft conversion. There are only 2 rads on that floor

 

[John.g]

Closing the TRVs (only) on the working rads is fine, re the two non working rads, I would suggest letting one fully open, then close one side of the other rad and see have you pressure at the vent then reopen it and shut the other side and see have you pressure at the vent from this side, repeat this with the remaining rad.
Draining down the whole system and refilling very slowly with the ball cock partly tied up and with any zone valves latched open can sometimes work.

 

[NODDYNODSVILLE]

Do you have to shut both valves on all the working rads. Because I tried shutting TRVs and leaving lockshieds open on working rads and still did not work.

Closing the TRVs (only) on the working rads is fine, re the two non working rads, I would suggest letting one fully open, then close one side of the other rad and see have you pressure at the vent then reopen it and shut the other side and see have you pressure at the vent from this side, repeat this with the remaining rad.
Draining down the whole system and refilling very slowly with the ball cock partly tied up and with any zone valves latched open can sometimes work.

Closing the TRVs (only) on the working rads is fine, re the two non working rads, I would suggest letting one fully open, then close one side of the other rad and see have you pressure at the vent then reopen it and shut the other side and see have you pressure at the vent from this side, repeat this with the remaining rad.
Draining down the whole system and refilling very slowly with the ball cock partly tied up and with any zone valves latched open can sometimes work.

Sorry to be a pain, but when you talk about pressure at the vent, do you mean where you bleed the rad, or the expansion pipe over hanging the header tank.
As you can tell, I’m not a plumber/heating engineer. DIY should stand for Don’t Involve Yourself. All I done was changed one rad, which is working fine.
On the forum, someone mentioned that the system might not be filled up. If I have water coming out of every rad, how do I check system is filled sufficiently.

 

[John.g]

No problem, I am talking about the rad vents in all cases, the system is or does appear to be "full" since you are ventintg water from the highest rad(s) vents.....Just be certain, look into the small tank in the attic and ensure that there is some water in it.
Re the problem rads, even though you are venting water, you don't really know if the rad is air locked on one side or not, so (even with boiler off) if you shut one side and if water keeps coming out of the vent then it is more than likely that there is no airlock from this side, shut this side off and open the other end and see if water keeps flowing from the vent then again it is fairly likely that you havn't an air lock from this end, repeat this with the other rad, I would then fire the boiler and repeat this whole process and see what you get.

 

[NODDYNODSVILLE]

No problem, I am talking about the rad vents in all cases, the system is or does appear to be "full" since you are ventintg water from the highest rad(s) vents...Just be certain, look into the small tank in the attic and ensure that there is some water in it.
Re the problem rads, even though you are venting water, you don't really know if the rad is air locked on one side or not, so (even with boiler off) if you shut one side and if water keeps coming out of the vent then it is more than likely that there is no airlock from this side, shut this side off and open the other end and see if water keeps flowing from the vent then again it is fairly likely that you havn't an air lock from this end, repeat this with the other rad, I would then fire the boiler and repeat this whole process and see what you get.

No problem, I am talking about the rad vents in all cases, the system is or does appear to be "full" since you are ventintg water from the highest rad(s) vents...Just be certain, look into the small tank in the attic and ensure that there is some water in it.
Re the problem rads, even though you are venting water, you don't really know if the rad is air locked on one side or not, so (even with boiler off) if you shut one side and if water keeps coming out of the vent then it is more than likely that there is no airlock from this side, shut this side off and open the other end and see if water keeps flowing from the vent then again it is fairly likely that you havn't an air lock from this end, repeat this with the other rad, I would then fire the boiler and repeat this whole process and see what you get.

Tried your advice, no joy, still getting cold water out of vent. I’m going to drain the system, and fill it the way you said, with the float tied up, and fill it slowly. Be back tomorrow or Wed.

 

[John.g]

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.

 

[SimonG]

What size pipework to the radiators?

 

[ShaunCorbs]

remove the rad and connect a hose to the rad valve either side

 

[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.