Double radiator with varying temperatures. 25 January at 12:54PM in In my home (includes DIY) MoneySaving 12 replies 249 views

Rusty190

I have a large double panelled radiator.
The 2 panels are very different temperatures to each other and both are hotter at the top than the bottom.
Front panel is very hot at the top and warm at the bottom.
Back panel is warmish at the top and tepid at the bottom.
Have had a power flush and clean out of whole central heating system recently.
This particular radiator had no heat at all prior to that.

I will get the plumber back to re-look again but in the meantime would appreciate all opinions as to what might be going on here and what may be done to fix this.

Robin9

Have you bled BOTH panels ?

FreeBear

And have all the radiators been balanced properly ?

It may be the lockshield needs cracking open a tiny amount (eighth of a turn at most) to increase the flow slightly.

Rusty190

There is only 1 bleeding connection point for both panels not separate ones for front and back, so, yes, both panels have been bled.

TELLIT01

Most likely cause will be a build up of crud in that radiator.  Ideally it needs to be removed and cleaned out.

Rusty190

FreeBear said:

And have all the radiators been balanced properly ?

It may be the lockshield needs cracking open a tiny amount (eighth of a turn at most) to increase the flow slightly.

Apologies but, I wouldn't have a clue where to look for a lockshield and, if I ever found one my dilemma would be which way turning it opens it and which way closes it?
I am assuming that my plumber did "balance" the radiators (another one of life's mysteries to me) after the power flush.

TELLIT01 said:

Most likely cause will be a build up of crud in that radiator.  Ideally it needs to be removed and cleaned out.

Would the power flush not have removed said crud from the radiator though?
Lots of smacking with a rubber mallet was also involved - of the radiators that is.

I don't know if this is significant but this radiator is the newest one on the whole system - approximately 5 years old.

Will_Riker

At the bottom of the radiator, there will be a valve at each end.  One valve will be either a thermostatic valve or a simple adjustment valve - either way, it'll have a knurled top to allow you to easy turn it.
The valve on the other end will be a smooth valve, not easily turned by hand - this is the lockshield valve.  You should see a small screw in the top of it.  Remove the screw, and the cap will pull off, revealing a little valve stem with (usually) a square or rectangular head.  Use a spanner or pair of pliers to turn that.  Anti-clockwise to open the valve, clockwise to close it.

The plumber probably won't have balanced the system after flushing it- there shouldn't be any need to balance after a flush.  However, the system should have been balanced after a new radiator has been added - has that radiator ever worked properly, or has it always had this issue?

The flush should have cleared it - though it's possible there was some really stubborn muck in there that needs addressing by removing the rad, taking it outside and flushing it through individually with a garden hose (not a particularly difficult job, though it may sound a bit daunting if you're new to plumbing DIY).

akira181

It's nothing to do with balancing, that's only if other radiators are getting hot while one or two (usually the furthest radiators from the boiler) are not getting hot or taking much longer to heat up compared to the others. You balance the system so the water flow is equal to all radiators and not just circulating around the closest ones. Generally it's only required for bigger systems and won't be necessary in a flat or small bungalow.

If it's cold at the top and hot at the bottom, there's air trapped in the radiator preventing the water from reaching the top and needs bleeding.

If it's hot at the top and cold at the bottom, your radiator is choked/blocked with magnetite and other central heating sludge, preventing water flow on the bottom.

A power flush (presumably carried out at the boiler?) will remove some sludge from the system (more if a chemical cleaner was added to the system and ran for a few days prior) but it will not effectively clear a heavily blocked radiator, which sounds like yours was. Lockshields have very small openings, even when fully open, so most of the sludge doesn't get removed due to the relatively low flow rates, unless the chemical cleaner was particularly effective and the power flush carried out for a long time.

Best way to clear a sludged up radiator is to isolate the rad, take it off the wall, and blast water through with a garden hose until the water runs clear. The radiator should be tapped with a rubber mallet, turned upside down, etc while flushing with the garden hose to get rid of all the sludge. Reattach to the wall, top the system up with inhibitor if not already done to prevent further sludge growth/accumulation, and it should be fine.

FreeBear

akira181 said:

It's nothing to do with balancing, that's only if other radiators are getting hot while one or two (usually the furthest radiators from the boiler) are not getting hot or taking much longer to heat up compared to the others. You balance the system so the water flow is equal to all radiators and not just circulating around the closest ones. Generally it's only required for bigger systems and won't be necessary in a flat or small bungalow.

Balancing of radiators is important regardless of the size of the system.

I suggested cracking open the lockshield based on experience  One of the radiators here that I balanced and adjusted to give a ~10°C temperature drop only ever got warm at the top. Cracked the valve open to give an 8°C drop, and it now gets well toasty.

Rusty190

This is all very helpful and I'm learning a lot from the discussion amongst you knowledgeable folk - thank you.
I should have said at the outset, the power flush was carried out as part of the service of fitting a new boiler.
He added 2 lots of chemical cleaner as he flushed and flushing went on for several hours.

Radiator did used to work well up until recently.

Would turning it off frequently, have contributed to sludge build up?

I suppose sludge build up would be a logical answer as this is a fairly big radiator (160cm x 70cm), and the rubber mallet slapping could only be applied to front panel as back panel is inaccessible when on wall.

I'll get him back to re-look at it and drop these suggestions into the conversation!

akira181

FreeBear said:

Balancing of radiators is important regardless of the size of the system.

I suggested cracking open the lockshield based on experience  One of the radiators here that I balanced and adjusted to give a ~10°C temperature drop only ever got warm at the top. Cracked the valve open to give an 8°C drop, and it now gets well toasty.

Naturally I cannot speak for every system but in the 8 years I spent as a heating and vent commissioning engineer, I generally found that small radiator systems (less than 7 or 8 rads) rarely needed balancing. Properly designed larger systems didn't need it either but As-Designed and As-Built usually aren't 1 to 1 and becomes necessary.

I'd suspect that your rad either had a minor bit of sludge restricting the channels at the bottom or the lockshield was too restricted to begin with. Both cases, opening the lockshield would fix it (until the sludge built up some more in case of the former) but that's just my guess without knowing your system.

Rusty190 said:

This is all very helpful and I'm learning a lot from the discussion amongst you knowledgeable folk - thank you.
I should have said at the outset, the power flush was carried out as part of the service of fitting a new boiler.
He added 2 lots of chemical cleaner as he flushed and flushing went on for several hours.

Radiator did used to work well up until recently.

Would turning it off frequently, have contributed to sludge build up?

I suppose sludge build up would be a logical answer as this is a fairly big radiator (160cm x 70cm), and the rubber mallet slapping could only be applied to front panel as back panel is inaccessible when on wall.

I'll get him back to re-look at it and drop these suggestions into the conversation!

Chemical cleaner ideally gets added a few days to a week before the old boiler is removed to allow the system to run and get up to temperature. It helps get the sludge loose/waterborne and makes it easier to flush out but not always possible if the old boiler is broken or the engineer too busy to visit (particularly in winter) just to dose. It's good that he used 2 lots but it wouldn't have been working at optimum efficiency as ideally it needs to be at temperature and takes some time to work. For a small system, I'd expect flushing to take at least 4 hours. All day for a large system.

Turning it off frequently wouldn't affect the sludge build-up. Sludge is usually oxidation from the pipework/rads, bacteria, and dirt. It happens more if there is no inhibitor in the system or if you have to frequently top the water up, introducing more oxygen into the system for further oxidation.

It's possible that sludge remained waterborne in the system after the flush and has accumulated in this rad, restricting the valve or channels within. Best bet is to get him out to flush again; ideally by taking the offending rad off the wall and directly flushing so you can get at both sides, rock the rad about, etc, but it's a big rad (~50kg dry) and probably a 2 man lift so he might not want to do it. (can be done solo but it's a nightmare)