Diagnosis of radiator problems

[PigletJohn]

This may prove useful now the weather us getting cold.

(My old post is ten years old so may perish)

"hot across the top, cools when turned down
may be badly sludged

heats all over, cools when turned down
correct behaviour

hot across the bottom, cools when turned down
is full of air, or badly sludged.

warm extreme bottom one side, cold elsewhere.
insufficient flow. Turn off ALL the others and see what happens. May improve if all rads are balanced

One side becomes hotter when other radiators are turned off and there is some heat across the bottom, but the top stays cold
air, or sludge, also poor flow

hot across the bottom, no noticeable change when other radiators are turned down
Air or sludge

hot all over, cools when turned down
Correct

If it turns out you have sludge (more common on old, open-vented systems), and you are fond of DIY...

I would recommend starting with a simple chemical clean. If you are fond of DIY plumbing it need only cost £20 for chemicals, plus two half-days of tinkering.

You will need to find a downstairs drain cock, and (probably) a small feed and expansion tank in the loft. Or a plumber or heating engineer can do it. You do not need to pay Gas Engineer prices because it is not gas work.

If you are fond of plumbing and strong, you can also take the rads into the garden and squirt a hosepipe through them.

I would also recommend fitting a magnetic system filter, to capture loosened sediment, on the Return pipe to the boiler. It is not a difficult plumbing job.

Preferably fit it before doing the clean as it will stop sludge moving into the boiler.

A chemical clean is not very intensive, but it will certainly do nothing but good. If more work is needed afterwards, it will not have made things worse."

Incidentally, the original Magnacleans were quite prone to leaks. The valves seem to be better now, and you can easily buy a replacement rubber ring to seal the cap, if necessary.

And if your radiators need Balancing...

"you probably haven't got a pipe thermometer, but the flow of water is meant to be slowed enough to give a 20 degree C temperature drop through each rad (otherwise all the hot water will rush through the easiest ones leaving the others cold) but a good rough guide is the flow (input) pipe should be "too hot to hold" and the return (output) pipe should be "too hot to hold for long"

Turn off the heating for an hour so all the rads are cold before you start.

Almost all the adjustment in a lockshield is in its first turn from shut, so screw them all down tight, then open the first one just half a turn and turn on the heating. Wait five minutes and see if it has warmed up. If so, leave it, and do the next. Don't adjust it by more than a quarter of a turn at a time.

If you haven't got time to do them all, turn down the hottest rads, and this will force water to flow through the coolest ones. But as I say, you have to turn the lockshield until it's almost closed to make any adjustment.

The rad in the room with the wall thermostat should be adjusted to heat up slowest.

If one of the rooms is relatively large, with a relatively small radiator, you can let it get a bit hotter than a large radiator in a small room.

If any of the valves starts to weep water round the spindle while you are working, screw it quickly either all the way shut, or all the way open, to stop the leak, and see about getting it replaced.

Have you got thermostatic radiator valves? If not, you will have to make further tiny adjustments

Interestingly, radiators are not balanced by opening up the cold ones, but by closing down the hot ones.

Thanks a lot for this post!
I have a question: two of my radiators (on different floors) are totally cold. They were working when the system was checked and restarted after a new boiler was installed. Then we close them because it was warm. After that, the other are working, and these two are not. We bled them a lot of water came out, and still nothing. These are old cast iron radiators with TRVs. I am pretty sure the system had a chemical clean because I have requested it, but I cannot be 100% sure because I wasn’t present then. Is there something we could do, or should we call the boiler guy?

second question: what does it mean “The rad in the room with the wall thermostat should be adjusted to heat up slowest.”? How do I do that?
Also, our thermostat is in a big living room with smallish radiators. If I need heating in the study or bathroom, I close the vales in the living room to not heat it up pointlessly. Is this correct? I think that we should change the TRVs to programmable digital to avoid this because it’s quite hard to manage.

Thank you for this @PigletJohn

We had a new boiler last year and following a power flush of every radiator (20+ in a big, old house) you can really tell the difference. Re-balancing has helped too.

@PinkCamelias "two of my radiators (on different floors) are totally cold"

Close ALL the hot ones. Do the cold ones now get hot? If so, the rads need to be balanced.

@PinkCamelias "“The rad in the room with the wall thermostat should be adjusted to heat up slowest.”

By balancing, adjusting the lockshield a little more closed. This will reduce the flow of hot water so it heats up slower.

@PinkCamelias "our thermostat is in a big living room with smallish radiators. If I need heating in the study or bathroom, I close the vales in the living room to not heat it up pointlessly."

A big room with small radiators will naturally heat up slowly.

The room thermostat should be in the room that you use most. If you turn off the heat in the room with the stat, the rest of the house will be heated indefinitely, or until you manually intervene. You can use the TRVs to manage the temperature in the other rooms, including turning them down if they are not being used.

What about a system that has evenly hot radiators and seems to work really well but sounds like an experimental steel pan band when it comes on?

@PigletJohn My parents have a late 1950s single pipe system that needs a clean through.
What wording do I need to use to find a plumber who is competent to do it? What questions do I need to ask?
Any advice very much appreciated.

Single pipe systems are not well thought of in ordinary houses. I suppose you will do best with an experienced independent engineer, not a large company or most younger people. Many people will advise you to change it to twin-pipe. I understand they are still used in USA and they have additional valves under the floor to adjust the bypass flow.

Personal recommendation from someone local whose opinion you trust is best. Parish Magazines often have small ads from local businesses. If they wear blue overalls and a cloth cap this may be a good sign.

If it is banging, this is probably coming from the boiler, especially if it is an old iron one with limescale deposits in the heat exchanger. These noises are called kettling, after the noise a scaled up kettle makes when it comes to the boil. It is caused by bubbles of steam forming, and collapsing, inside. There are chemical treatments to deal with it.

Other noises, heard mostly under the floor in various rooms, often ticking, clicking and creaking, are caused by the pipes expanding and contracting with heat, and rubbing against the joists. It is easily prevented during installation, by putting felt round the pipes, but more of an effort later as you have to take the floor up. Radiators also do this. They are supplied with little plastic U-shaped sliding spacers to go on the brackets, some ignorant people fail to fit them. They can be added later but you have to lift the radiator off its brackets.

Bleeding Radiators

When radiators need bleeding, it is because they have air (gas, actually) in them. It floats on top of the water, and because the tops of the radiators have no hot water in them, you can easily feel with your hand that the tops are cold.

If that is not the case, they do not need bleeding and it will not help.

Very timely advice for me today, and I really appreciate you sharing your knowledge. Thank you @PigletJohn

@PigletJohn Thanks; at 94 and 88 they don't want the disruption of repiping, and the house will be demolished when they move out (happens to all the older houses in the road) so no point doing for resale value.

I'll hit the local Facebook and do some ringing round.

Love your threads PJ.
Dh is cleaning/flushing ours through, all ours, next week.

Thank you very much @PigletJohn !

Thank you for posting ❤

I had a heating guy over to look at the radiators that don't work. Turns out the valves need to be replaced. I asked him about installing smart TRVs and he wrote down all the rads in the house and we discussed on which ones they would make sense. He will send me an offer tonight. I know that this would be a Honeywell system (thermostat and TRVs). The boiler is new, Vaillant, installed by the same guy this autumn, no problems with it. Not UK, so presumaby different brands available here.

I've read about the smart system and i very much like the idea of beimg able to set the heating zones and save money. The house is big and naturally some rooms are used much less than others.

Is there anything I should be aware of? How best to design the zones? the thermostat would be in the living room so he suggested normal valves on rads there, but smart valves in the adjoing dining room; normal valve in the kitchen. @PigletJohn and of course anybody who may have any advice.