Radiator warm at the bottom

[vw754]

Ive flushed my central heating system today, used fernox......after 7 years, just as a precaution, water was clear yellowish, after filling the system, still came a clear yellowish colour, when i say yellow ish i mean very pale yellow.
Had a new extension a couple of years ago, and 2 pipes coming from upstairs to the downstairs radiator where sent to the new radiator in the new extension, only thing was the plumber used reducers.... 15mm to 10mm,hid pipes behind wall and into the new radiator, reducers used both ends...... That new radiator always seems warm at the bottom, but red hot at the top...... Is it because of the reduced 10mm to that radiator?
Boiler is a Worcester, i have 10 radiators, in the house, all radiators are double, around 3-4 feet long,and a towel radiator..... If that makes a difference,....... Someone said to me, they need balancing????.... Ive tried that but still seems same

If i turn upstairs radiator completely off via thermostat, which is directly above the radiator in question, then the radiator in question, does get a little better.

 

[Gasguru]

If i turn upstairs radiator completely off via thermostat, which is directly above the radiator in question, then the radiator in question, does get a little better.

Lost me there...the new rad is in its own zone?...surely the room stat is not installed above the rad?...why would it get hotter when you turn the stat off?

It sounds like there's insufficient flow through the radiator...you need to carefully balance the system to give a similar temperature drop across the flow/return pipes on each rad.
If you really can't get it to work then either the pipework is too small or something else...

 

[vw754]

Own zone yea, what im saying is when i turn upstairs rad off, the bottom one in question is getting a tad warmer at the bottom....... So balancing then?

 

[MeldrewsMate]

Clearly when the upstairs zone has no flow there is increased pump pressure to the rest of the system, so your last symptom would be consistent with this.
I assume plumber used plastic pipe to new rad in the extension? 10mm plastic should be OK for one rad, but beware that the pipe stiffeners he may (or may not) have fitted will reduce the bore further, and are a 'filter' for debris, and this could have partially blocked your pipe.
If you're up to it (and it IS plastic) I suggest the following actions:

1. Close both valves to that new rad.
2. Disconnect the rad and remove it for now.
3. Open each rad valve in turn, discharging its contents into a bucket, about a litre each side should do it.

Do they each flow at about the same rate?
Inspect the discharged water. Did any crud come out? Any big bits?
Did an initial surge of water drop to a trickle within seconds?

4. Flush radiator with a hose if necessary, again looking for large bits of debris.
5. Reassemble and test.
6. Report back (we all have egos, and want to know if we're right!).

MM

 

[vw754]

Clearly when the upstairs zone has no flow there is increased pump pressure to the rest of the system, so your last symptom would be consistent with this.
I assume plumber used plastic pipe to new rad in the extension? 10mm plastic should be OK for one rad, but beware that the pipe stiffeners he may (or may not) have fitted will reduce the bore further, and are a 'filter' for debris, and this could have partially blocked your pipe.
If you're up to it (and it IS plastic) I suggest the following actions:

1. Close both valves to that new rad.
2. Disconnect the rad and remove it for now.
3. Open each rad valve in turn, discharging its contents into a bucket, about a litre each side should do it.

Do they each flow at about the same rate?
Inspect the discharged water. Did any crud come out? Any big bits?
Did an initial surge of water drop to a trickle within seconds?

4. Flush radiator with a hose if necessary, again looking for large bits of debris.
5. Reassemble and test.
6. Report back (we all have egos, and want to know if we're right!).

MM

Thanks for your great information and your help, there was no cruds, no black sludge or anything, all there was, was pale yellow clear looking water with the most teeniest black bits in there, very very tiny,...... I have adjusted all the valves, going around the house, opening all valves about 3 turns max, seems like its a lot better.
As for pipes, he used reducers on the existing pipes and used copper pipes.

15mm pipes fitted with reducers, then 10mm pipes going to the radiator, all copper pipes.

 

[Gasguru]

You need to balance it...google it.
You might have to throttle down some smaller rad lockshields (and towel rails) so they're only open an 1/8 of a turn...especially if they are near the pump....it can be that critical.
Open 3 turns is pretty much full flow.

 

[vw754]

You need to balance it...google it.
You might have to throttle down some smaller rad lockshields (and towel rails) so they're only open an 1/8 of a turn...especially if they are near the pump....it can be that critical.
Open 3 turns is pretty much full flow.

THANKS VERY MUCH

 

[Gasguru]

Remove TRV heads/open up wheelhead valves, set the lockshields to a sensible setting based on likely pipe run/size/distance from pump.
Start with the boiler heating temp say 40 degrees.
Now run around the house and mark the flow side of each rad..ie. the hotter pipe (if the rads heat up too quick (say the lockshield is open too much) it can be difficult to determine the flow/return pipes), you're aiming for an equal temp drop across all the rads (and hence the same return pipe temps). Ideally around a 10 to 20 degrees drop (it depends on the weather/heat loss etc).
Once the rads come up to temp turn up the boiler flow temp so you can tweak the valves again.
Use your hands to feel the flow and return pipes at each rad and the surface to get an idea of the warm up.
You may have to let the system cool to have another go and refine the settings.