Cold Spot on Radiators

Richie7

Hi 

Just had a new central heating installation, and two of the radiators have cold spots at the bottom. An engineer came a week after it was done and flushed the system. I noticed these cold spots before they did that however. I think the engineer hoped the flush would fix it. Bleeding has failed as well.

So the question I have, is do I have faulty radiators? Bearing in mind they're meant to be brand new.

Any suggestions perhaps?

Much obliged as always.

FreeBear

Heating kicked in a little while ago, and I've just had a feel of my radiators. Bearing in mind, the system had only been running for ~15 minutes, the sides & top of the radiators were "hot", but the middle bottom was noticeably cooler to touch. Running the system for a longer period (an hour or more) would see the whole radiator getting hot.

Has your system been properly balanced and the pump speed set accordingly ?

Richie7

Yes as far as I'm aware. All the radiators work splendidly in turning on and building heat together. And all of them except the two in question have heat spread evenly across their surface.

But even after the heating has been on for an hour, these two radiators have those cooler spots, whereas the others do not.

This surely can be rectified?

It's a shame because we're very pleased otherwise with how things have been done.

jonnydeppiwish!

As previous poster, sounds like they need to be balanced. Common thing to do post new install/overhaul

ThisIsWeird

Hi Richie.
I'm concerned that your installer came out a week after it was done to carry out a flush.
What do you mean by a 'new CH installation'? What is 'new'?
As suggested above, the most likely cause is a lack of system balancing. I presume most of the rads have TRVs on them? Ok, fire up your CH as normal until it's 'hot' - a good half hour or so. Now fully open the TRVs on the two 'cool' rads, note the rad temp so you can compare, and then close a good 4 or 5 other rads right down to off.
If it's a lack of balancing, the cool rads should heat up more.

Richie7

It can't be a system balancing issue. The rads in question heat up just as well as the other rads, and get just as hot. So it can't be the TMVs either.

If you imagine each radiator has 6 spots - top left, right and middle, bottom left, right and middle. It's only the bottom middle on one, and bottom left on the other that are cool. The other spots are all scorching hot.

I believe I've either got 2 faulty rads, or there's some kind of blockage in those spots. That they're both at the bottom seems to suggest that based on what I've been reading since I posted here.

There simply can't be another explanation can there. Unless someone has one of course.

ThisIsWeird

Richie7 said:

It can't be a system balancing issue. The rads in question heat up just as well as the other rads, and get just as hot. So it can't be the TMVs either.
If you imagine each radiator has 6 spots - top left, right and middle, bottom left, right and middle. It's only the bottom middle on one, and bottom left on the other that are cool. The other spots are all scorching hot.
I believe I've either got 2 faulty rads, or there's some kind of blockage in those spots. That they're both at the bottom seems to suggest that based on what I've been reading since I posted here.
There simply can't be another explanation can there. Unless someone has one of course.

Ah, I see.
Is the whole system new? If not, what's been replaced?
When they carried out this 'flush', what did they do, and what was the result? Did they 'catch' anything?

In general, tho', yes, a cold mid-bottom would indicate sludge, and that could also be the case in the left-bottom if that's the l/s side?
Some rads come, or used to, with removable rubber bungs in the centre of the bottom tube, to force the water to go up and around, but I've no idea if that's still the case (except in tall column rads).
Anyone know? 
Anyhoo, answers to Q's, please. 

FreeBear

Richie7 said: If you imagine each radiator has 6 spots - top left, right and middle, bottom left, right and middle. It's only the bottom middle on one, and bottom left on the other that are cool. The other spots are all scorching hot.

I believe I've either got 2 faulty rads, or there's some kind of blockage in those spots. That they're both at the bottom seems to suggest that based on what I've been reading since I posted here.

If the radiators are scorching hot except for the one spot at the bottom, it certainly sounds like a fault. Having two new radiators being blocked by sludge is unlikely so soon after installation. Having two with a manufacturing defect is unusual, but not improbable. Ideally, the radiator needs removing, and an endoscope poked inside to see what is going wrong. Few people would have such a tool, although you can get small USB bore cameras from ebay/amazon for less than £10..

Side note - Modern heating systems should have a maximum design flow temperature of 55°C. If you are running scorching hot, you won't be getting good efficiency out of the boiler and you are wasting money.