Radiator heat - bamboozled.

[asnoop20]

I've a working system at 2 bar but a single column radiator which will not heat up unless all other radiators are heavily restricted. By restricted I mean so much the boiler cycles the heat due to minimal flow and the other radiators don't get hot. Obviously this points to blockage between the flow/return pipe, valves or the radiator itself.

The radiator is brand new one of these common models - https://www.ebay.co.uk/itm/391972553871

There is (or was no air in the radiator at all). I've now disconnected the radiator and the water has came out both ends easily. It's clean as the system has had several flushes with various radiator changes over the past 6 months. Then I opened the values expecting one would have low pressure and water has came out fine of both!

The inlet heat I'm pretty sure was connected to the left side which is correct I believe for these radiators although others say it doesn't matter. The valves are basic non TRV ones so it wasn't them either. The 10mm copper is only about 6M in total not really enough to be too long to act as a restriction I think, plus I have another which is almost an identical length and same radiator and it doesn't have the issue at all - red hot!

Any ideas as I'm now out of them!

 

[terryplumb]

Is the rad fitted upside down ?
Can you see a baffle, looking through the inlet port of whichever side of the rad that should be connected to the flow ?
If you close off every other radiator by it's TRV ,EXCEPT the smallest one on the system ,does problem rad heat up ?

 

[asnoop20]

I found a diagram which might suggest direction is important "blocker"

Without any flow it's difficult to know which pipe is flow as used PEX which isn't getting warm. However if I turn the filler on (system now empty) water comes out one valve/end pretty much immediately but with the other it's a lot of air and then water eventually. Can I take it the filler adds water to the flow side so the immediate side will be flow?

If so that's my issue, inlet/outlet are reversed.

 

[asnoop20]

Is the rad fitted upside down ?
Can you see a baffle, looking through the inlet port of whichever side of the rad that should be connected to the flow ?
If you close off every other radiator by it's TRV ,EXCEPT the smallest one on the system ,does problem rad heat up ?

Standard way up.

If I close or heavily restrict every other radiator yes it does heat up but not well. The boiler starts cycling, so it's set at 65c but it goes down to like 40c and tries then gives up for a bit then comes on. I assume the flow isn't enough for the boiler and it's protecting itself.

Not sure what a baffle will look like but heading outside with the torch now. I have connected the hose to both sides and water is coming out freely but of course it's at almost zero pressure and zero heat so that might mean nothing.

 

[terryplumb]

The baffle is just a physical diverter to direct the incoming flow upward.
If you want to establish which pipe is the flow, connect a piece of pipe between the valves and run heating, whichever pipe heats first is the flow.

 

[asnoop20]

I've looked through and I do see what looks like a round disc where it says 'blocker' in the diagram. Is it heat based or is it literally just a block to force water upwards?, in which case it wouldn't matter which was inlet/outlet?

 

[terryplumb]

Is the " blocker / diverter" nearer to one side / inlet port. If so ,that port has to have the flow connected to it.

 

[Madrab]

or is it literally just a block to force water upwards

It's to divert the flow upwards and stops the water just running along the bottom of the rad and then up. The rad will not heat up properly if it's reversed, the flow needs to be on the baffle side of the rad.

Is the system microbore? 10mm pipe?

 

[asnoop20]

Established the flow is on the inlet side. I was hoping it wasn't!

 

[asnoop20]

It's to divert the flow upwards and stops the water just running along the bottom of the rad and then up. The rad will not heat up properly if it's reversed, the flow needs to be on the baffle side of the rad.

Is the system microbore? 10mm pipe?

15mm.

It's 22mm to the fork, then 6M of 15mm to the rad. At the same point it forks it goes 15mm to three more radiators with a lot more length of pipework so I don't think they are giving so little resistance that it's always bypassing this one. Still I'll try shutting them off completely now and see if it forces water to circulate. Still going to have the boiler cycling though. As far as I can tell water just hates to go along this route!

 

[Madrab]

If there's 3 rads, including the column being fed from 15mm, then that is probably your issue. Water is lazy and will always take the path of least resistance, there is a fair amount of resistance in these designer columns, especially given their increased height and design and therefore the water will favour the other rads before that one. They are such a terrible design IMHO.

Balancing will probably be required.

 

[asnoop20]

I believe you're right but I've balanced the rest to the point they're closed.

At the moment I have the two identical rads connected. Both are next to the same fork point with the same amount of pipe roughly. All other rads are off.

The other rad is getting hot easily, so I make it's valve only one turn from closed to balance and it's still hotter than the other. I then close the valve so only the one problem radiator is on. The boiler then starts flow erroring, coming back on every so often.

 

[Madrab]

The boiler then starts flow erroring, coming back on every so often

Does it give an actual error, what boiler is it and if there is one what error is it?

The boiler will modulate, though it'll only modulate down so far before it shuts down. So boiler size dependent it would need more than one or 2 rads open for it to just tick over.

You mentioned that it's 6m of 10mm, from a 15mm branch from the main 22mm backbone? That 15mm is already feeding 2 other rads and the 2 other rads have 15mm up to the valves? If that's the case then I would suspect that's the problem, there's just not enough positive flow for an 1800mm vertical tube rad without some seriously fine tuning

I don't fit 1800mm designer columns from one 15mm feed with 10mm pipe, as I can just about guarantee that the vertical rad won't ever heat up properly. Ask me how I know