New Rad not getting hot, single pipe CH system (partial)

[matt-l-p]

Hello, i've posted on here as it seems there are a few single pipe experts.

I've installed a big column rad with normal valves (no TRV) on a single pipe system, i have done this in 2 other rooms with good success and continue to get very hot. The rest of the house is on a 2 pipe system and works well.

When i converted the rest of the house to a 2 pipe system i couldn't do the remaining 3 rads on single pipe system as the rooms were completely finished with oak tongue and groove flooring and the rads were working well.

The rad i'm having an issue with has never worked great and i thought a big column rad might help, but it hasn't. The flow into the rad is getting really hot but there seems to be not much flow, after 2 hours it still isn't getting up to temperature.

I've found an old picture before i replaced the floor and subfloor and it looks like the 15mm return the the 1 pipe system is on a tee piece on a corner, i'll attach a picture.

could it be the water is just rushing past that tee piece as it's on the corner, so no flow for the rad?

Any help would be appreciated.
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This is the current downstairs set up
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Please see new proposal picture, would this work ok?

 

[Aquarius]

Quite possibly just a balancing issue, I’m not 100% with single pipe (not had the pleasure of working on them). Also, these column rads, not sure if there’s a certain way to hang like vertical ones and baffles?

 

[matt-l-p]

Thanks. It's a horizontal one, so doesn't need baffles.
I've tried shutting other radiators and made no difference, also tried for air locks.
Bit of a mystery, I think I could run in a plastic return pipe to the boiler without much damage to the oak floor, just wanted to make sure that would work.

 

[Gasmk1]

have you pipe top flow bottom return as single pipes use gravity flow for the rad

 

[matt-l-p]

No I've not tried that yet, I have 2 other column rads on the single pipe system and they work fine both piped on bottom.

 

[Last Plumber]

Where is the pump on the sketch?
Can you add it in?
How have you converted the rest of the house to two pipe? Can you draw a sketch of that?

 

[matt-l-p]

Where is the pump on the sketch?
Can you add it in?
How have you converted the rest of the house to two pipe? Can you draw a sketch of that?

It does have a pump just after the boiler outlet, then tees off one feed upstairs and downstairs, then the return from upstairs taps into the return to the boiler

 

[exedon2]

I first fixed many hundreds of one pipe systems in early 70s ( council upgrades) rad connection was always T on branch. So your layout with connection on end is not ideal so probably why it's never been great.
Should also mention lots of horizontal column have baffles!

 

[matt-l-p]

Thanks , much appreciated. It must be the Tee on the corner. Is a baffle the same as a diverter. The instructions says only use them on rads over 1000mm high, so I didn't put them in

 

[exedon2]

Maybe just check with rad manufacturer re diverter on a one pipe?
I've installed this type of rad as a heat leak and manufacturer said diverter was needed . Remember on a one pipe heat goes into rad by gravity.
One more thing your rad valves are full bore? I've seen some that are really quiet restrictive.

 

[matt-l-p]

I will check with them thanks, yes the valves are full bore. I think running the return pipe to the boiler will solve it

 

[Chuck]

Thanks , much appreciated. It must be the Tee on the corner.

I'd want to replace it with an elbow and then tee-in the radiator return a few inches downstream of the new tee. One-pipe systems are always a bit touch and go, which is why converting to a two-pipe configuration is the default solution to most problems.

 

[matt-l-p]

I've done what was suggested with the Tee on the left, and still isn't working well. Have tried everything now. Deffinetly no air locks. The feed pipe in is red hot, just isn't Flowing through

 

[Brambles]

If the flow is red hot, you have flow - just a restricted return

 

[matt-l-p]

Thanks, I've run in a new return pipe for the rad straight to the return on the boiler. Doesn't make sense. It slowly gets warm same as before, just Luke warm and takes 2 hours

 

[Brambles]

Is the return hot?

Are you sure that there are no restrictions in the radiator and the baffles correctly fitted

 

[matt-l-p]

The return is not hot, only Luke warm after been in for 2 hours. I've not fitted the diverters as the instructions said only fit on rads about 1000mm height. Have been trying to ring Nordic but no answer . Maybe an issue with the rad as I have other brand columns that work fine

 

[SimonG]

You're not getting enough gravity circulation within the radiator. Pump does nothing but circulate the heat around the one pipe loop. Then gravity takes the hot water into the radiator.

Does the pipe off the single pipe loop rise all the way to the radiator?

 

[matt-l-p]

So the feed from the single loop is a tee, and rises by 2 inch untill it hits the elbow then straight up into the rad, the length from the Tee to the elbow is about 300mm

 

[Brambles]

Three points:

Is the rad piped correctly for a one pipe system?

Is the valve correctly sized and suitable for a one pipe system? A normal TRV generally has too small an orifice - my money is on this point.

Are you sure than none of the plastic protective end caps have been pushed into the radiator?

 

[matt-l-p]

Thanks
I have 2 other column rads on the 1 pipe system, which are both piped into the bottom of the rad and work fine, so that's what I did with this, I know you can put the feed into the top of the rad, buy can't see it making any difference as it is so poor right now.

The valves are what I have used previous with success, manual angles valves 15mm, which seem to be full bore and not restrictive.

I unpacked etc myself so pretty sure there isn't any bungs etc in there

Thanks for your suggestions, and open to suggestions

 

[Gasmk1]

there is a big difference between the bore on a normal try and one designed for one pipe as the one pipe one uses gravity to feed the rad not the pump your flow is bypassing the rad.

 

[matt-l-p]

Thanks, has anyone got any links for single pipe system valves ? Can't find any online

 

[Gasmk1]

Danfoss Randall RA-G Single Pipe TRV Body - https://www.heatingcontrolsonline.co.uk/danfoss-randall-rag-single-pipe-trv-body-p-1195.html they are not cheap

 

[matt-l-p]

Thanks I've found the lockshield too, are they suitable for 15mm pipe, or have to change to 22mm ?
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Thanks everyone, thought I'd give you some feedback. I converted it to a 2 pipe system, 22mm feed in and guess what it still didn't work !
So I put in the baffle/ diverter and now works
Should of put it in to start with but the instructions said not to. Oh well lesson learnt.

About 3 days on it and a few trips to Screwfix haha