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New Radiators Not Working

View the thread, titled "New Radiators Not Working" which is posted in Central Heating Forum on UK Plumbers Forums.

Gidders

Gidders

In May I had my garage converted into a room & the builders plumber A, fitted a new radiator in there & moved the one in the hall

In June my plumber B, fitted a new gas boiler.

Now I've had the central heating on I've found the 2 new radiators don't heat up - all the other radiators in the house get red hot.

A is saying that B has left an airlock in the system - B is saying that A hasn't fitted the new rads correctly.
  • I have bled the new rads & there is no air in them
  • The pipe to the inlet valve of the hall rad gets hot but the rad doesn't
  • If I shut down all the old rads, the new rads get hot, although not as hot as the old ones
  • I've left the system running for 2 hours
  • After getting the new rads hot, if I open the old rads, the new ones go cold
  • The new rads are plumbed in 10mm pipe, all the old system is 15mm
Any suggestions what the problem is please
 
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For a start guy who fitted boiler should have made sure all radiators worked before leaving job. As many pictures of install boiler ect as you've got please.
 
Open up the lockshield valves on the opposite end of each rad, maybe they haven't been balanced properly, open them right up and see if the rads get hot. If that works you'll need to balance them, I think there's a radiator balancing thread on here somewhere.
 
Sounds like not balanced correctly also how many rads do you have in the house ?
 
There are 9 rads inc the new one & replaced one.

I suspected a balancing issue - would the fact that the newly fitted rads being on 10mm pipework vs old rads on 15mm pipework cause that sort of problem?
 
Yep as 15mm will flow easier than 10 mm close all the lockshields shut and open the 15mm ones 1/4-1/2 of a turn the 10mm ones 1/2-3/4 of a turn if you get some that are slow / not heating up open it a bit more
 
Gidders said:
In May I had my garage converted into a room & the builders plumber A, fitted a new radiator in there & moved the one in the hall

In June my plumber B, fitted a new gas boiler.

Now I've had the central heating on I've found the 2 new radiators don't heat up - all the other radiators in the house get red hot.

A is saying that B has left an airlock in the system - B is saying that A hasn't fitted the new rads correctly.
  • I have bled the new rads & there is no air in them
  • The pipe to the inlet valve of the hall rad gets hot but the rad doesn't
  • If I shut down all the old rads, the new rads get hot, although not as hot as the old ones
  • I've left the system running for 2 hours
  • After getting the new rads hot, if I open the old rads, the new ones go cold
  • The new rads are plumbed in 10mm pipe, all the old system is 15mm
Any suggestions what the problem is please
Click to expand...
NO air in rads is not the same as air in the main circuit. New boilers have low pressure pumps so often between 1-1.5bar. Any air in the system is always going to be at atmospheric pressure i.e. 1 bar. So fighting 1bar with a system that is 1.5bar before losses is never going to happen. You only have 2 options (forget this whole balancing thing, that was in the old days before variable speed pumps) You have to remove air by hiking up the pressure (to the point before the relief valve kicks in) to 2.75 bar so you can fight the air lock or you need to do a full re-circulation i.e. push water through until it has been round ever rad and pipe bend/high point. And before I hear the siren call of "the joints will burst" consider this. If your pipework cannot handle 3 bar then the problem you have is minor compared to the cost of what you have to do to fix the underlying pipe problem.
 
hometech said:
NO air in rads is not the same as air in the main circuit. New boilers have low pressure pumps so often between 1-1.5bar. Any air in the system is always going to be at atmospheric pressure i.e. 1 bar. So fighting 1bar with a system that is 1.5bar before losses is never going to happen. You only have 2 options (forget this whole balancing thing, that was in the old days before variable speed pumps) You have to remove air by hiking up the pressure (to the point before the relief valve kicks in) to 2.75 bar so you can fight the air lock or you need to do a full re-circulation i.e. push water through until it has been round ever rad and pipe bend/high point. And before I hear the siren call of "the joints will burst" consider this. If your pipework cannot handle 3 bar then the problem you have is minor compared to the cost of what you have to do to fix the underlying pipe problem.
Click to expand...
The new rads get hot when all, the other rads are closed off. Could there still be air in the main circuit in this instance?
 
May be worth checking the pump settings as well, if settable, as it may be set to some very low variable setting as suggested above.
 
Gidders said:
The new rads get hot when all, the other rads are closed off. Could there still be air in the main circuit in this instance?
Click to expand...
Now I'm not a qualified heating engineer with an NVQ but I do hold an MEng in electronics and I'm certified engineer through the engineering council so understand that what I say cannot possibly compete with an NVQ plumber but this is based on my personal experience in my home.
Large pipe run, air trapped. Cannot remove the air despite placing air vents in the pipework. My symptoms were radiators would work then they would not and they would alternate back and forth.
I had increased the pressure but the losses meant it could never reach the offending section of air. As I operate with low temperature heating, I decided to add an air vent in the offending section in the form of a large radiator. These videos of the commissioning of the large radiator might SOUND familiar to you. Video1 is radiator getting its first fill from the main 22mm primary pipe where I suspected the air lock was. Video 2 is opening the lockshield. Long story short, air gone, noise gone, system fine. 4 separate heating engineers had no idea what was happening because "they had never seen that before" LOL
In conversation with a retired plumber (some would say heating engineer) who specialised on schools and churches heating systems told me that it often took twice as long as the install job to remove the trapped air.
 

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hometech said:
Any air in the system is always going to be at atmospheric pressure i.e. 1 bar.
Click to expand...
You are mistaken. It'll be at the same pressure as the water that surrounds it. In an unvented system, which is what I believe we are discussing, it'll be somewhere in the range 2–3bar (absolute). For for a vented system, the pressure is only 'atmospheric pressure i.e. 1 bar' at the top, i.e. the location of the free liquid surface in the expansion tank.
 
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scott_d said:
There has been no mention of the make/model of boiler or if the pump is even inside it.
Click to expand...
If the boiler is less than 5 years old
Chuck said:
You are mistaken. It'll be at the same pressure as the water that surrounds it. In an unvented system, which is what I believe we are discussing, it'll be somewhere in the range 2–3bar (absolute). For for a vented system, the pressure is only 'atmospheric pressure i.e. 1 bar' at the top, i.e. the location of the free liquid surface in the expansion tank.
Click to expand...
so as you increase the water pressure you increase the air pressure making air impossible to remove from any system ever. Thanks for that. Just out of interest, how does that work with boyle's law? I've added a BBC bitezie for reference Volume and pressure in gases – the gas laws - Temperature and gas calculations - GCSE Physics (Single Science) Revision - BBC Bitesize - https://www.bbc.co.uk/bitesize/guides/zc4xsbk/revision/3
 
hometech said:
If the boiler is less than 5 years old

so as you increase the water pressure you increase the air pressure making air impossible to remove from any system ever. Thanks for that. Just out of interest, how does that work with boyle's law? I've added a BBC bitezie for reference
Click to expand...

You don't seem to understand the difference between 'pressure', which does not affect the motion of bubbles, and 'pressure gradients', which do. In this context, Boyle's law tells you that as the pressure in the system water is increased the bubbles of trapped air shrink in volume.
 
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