1 Rad, hot at top only

[DocD]

Hi, My parents are having a problem with an additional RAD on their system. All other Rads are fine, this one get fairly hot at the top, cool at the bottom.
Rest of system is on 15mm copper, this one is micro-bore! Also looks like feed is ok, but return goes into the return from another Rad, not into the main return.
Is there anything which can be done and would either of these inconsistences cause the problem?

 

[MANDATE]

I'm wondering if this really is a fault? surely to get hot at the top it must have been hot at the bottom.
I'm fairly sure I've had the same thing, when the room temperture gets satisfied soon after putting the heating on, or some time after the heating is turned off I find a difference between top and bottom of the radiators.
I'll be checking this out tomorrow.
I can only think of sludge in the radiator or could the inlet valve be at the top and outlet valve be at the bottom opposite corner making it difficult for heat to reach across the bottom.
If inlet and outlet are top and bottom on same side that could starve the opposite side and create this I would think.
I think I would feel all over the radiator when it is being switched on to establish which parts are getting hot and whether there are areas that never get hot.
I think I understand why you have had poor response, you've got the experts baffled.

 

[DocD]

Both inlet and outlet are at the bottom (opposite ends of rad)

A guy from British Gas said it wasn't right becasuse it was plumbed wrong but didn't say why!

To me it seems like it isn't getting enough flow, same sort of effect as if the boiler has only just come on, warms at the top first and the heat then moves down the rad. only in this case it never reaches the bottom. When I was over there at the weekend the boiler had been on for over an hour, all other rad were too hot to touch but the return pipe from this one was aired and the bottom half or so of the rad was still cool, not even warm let alone hot..

Would the fact the feed comes from the main feed, but the return goes into another rads return before going into the main return cause this sort of problem.

 

[Porker]

Sounds like the classic case of sludge build up. You may get slightly less flow with microbore and this has allowed it to accumulate. This can be flushed out though it is a pain to do. If rad. is hot at bottom near inlet and outlet but has a sort of cold triangle profile (imagine a hill of sludge with the highest point in the middle of the rad) then this is the classic symptom.)

I had this problem with one of mine.

My only other guess is that the balancing is way out. Turn off all the other rads in the house to force the flow through just this one to see. Count the turns in case the system has already been balanced to allow you to put it back as it was.

 

[MANDATE]

I would not think the layout of the inlet or outlet pipe is the cause but the fact it is 10mm pipe whilst the remainder is 15mm does suggest the radiator will be starved whilst others are not.
Replacing the pipe with 15mm seems the answer
You could try re balancing the whole system as suggested, by PORKER which would in effect mean slightly closing the lockshield valves on all radiators (except the problem one)thus restricting the flow and allowing more flow where it is needed.
You could turn all the radiators off except the problem one and the one which infuences the room stat, then slighty close the lockshield valve on this one a bit at a time until the problem radiator gets fully hot, then ajust the others accordingly.
Let us know how you go on!

 

[DocD]

Thanks for the suggestions, it could be a couple of weeks before I go over again, I will check for the triangle of sludge, then try the balancing first as this will make least mess. I will let you know how it goes - thanks.