One pipe radiator system

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It's simple physics. With a one pipe system, the water is pumped around the one pipe loop, meaning that because the radiator inlet and outlet pipes are connected to the same pipe they receive the same pressure from the pump, as a result, the pump can't force the water through the radiator in the same way a two pipe system does.

One pipe systems rely on the gravity principle of hot water rising and cooler water sinking to circulate through the radiator. This means to work the radiator ideally should sit directly atop the one pipe. The one pipe can of course be re-routed so that it passes directly below the new radiator.

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If there is a slight horizontal distance away from the one pipe, (ie it's not directly above) through a wall for example, the pipe must be inclined upwards and the horizontal distance kept as short as possible.

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What you can't do is have the two radiator pipes from the 'one pipe loop' running horizontally and through bends before reaching the radiator because the pump pressure on the flow and return pipes is the same it isn't able to force the water through the radiator.

If you re-route the one pipe loop so that it passes directly below the radiator, with the pipes going directly vertically in and out of the radiator above, all will be well.
Hi. Could this be why my new radiator is only getting warm. Would it help if sloped the outlet pipe back in to the one pipe??
The outlet pipe is the nearest in the pic, that outlet pipe is warm as It looks like it’s taken the least resistance for the water to take (it’s a smaller tee height)
 

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Yes, that'll be exactly why.

As per the forum rules, can I suggest you start your own post and link to this one, it avoids confusion over who's asking and answering what.
 
Hi.
my new radiator is only getting warm. Would it help if sloped the outlet pipe back in to the one pipe?? To help with gravity and flow
The outlet pipe is the nearest in the pic, that outlet pipe is warm as It looks like it’s taken the least resistance for the water to take (it’s a smaller tee height)


Thanks.
 

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I would personally had the tee's further apart.
Is that a normal trv? strictly speaking one pipe systems require a different trv eg danfoss ra - g standard ones are too restrictive.
 
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I’m pretty sure it’s a standard trv.
The rad is getting to 44 degrees. Would moving the tee further along and sloping it down into the one pipe help.
Thank you
 
I'm old enough to have installed one pipe systems back in day we would have run 22mm in a loop under rad that avoids the collection of elbows.
Some of that type of rad are flow specific having a baffle in bottom run.
Maybe fit a standard wheel head instead of trv to see what happens?
 
Thanks
It’s been connected up as per the flow and return stickers.
Do you think sloping the pipe back into the one would help?
If necessary I will have to put a 22mm loop under the pipe and tee off ?
Thanks
 

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