one cold radiator but no valve tops!

[emma_middlebrook]

Hi all

I'm a total beginner when it comes to anything like this but have tried reading up in a DIY manual plus read the uk.diy faq and have attempted a little investigation today.

Six radiators in the flat. All but one heat up quickly (within a few minutes). Furthest from boiler (24kW) only gets a bit warm at the top even after central heating has been blasting away for fifteen minutes.

So, just to limber up, I've increased the pressure when the system is cold to 1.2 (it was 0.8).

When it's on, rises to 1.4. From what I've read, this is about right.

Also attempted to bleed the radiators but there is absolutely no air in any of them as water spurts out immediately.

Took 1/2 pint sample of water from nearest radiator and furthest one. Sample water looks the same - a few little black specks but a clear, yellowy colour which I presume comes from the corrosion inhibitor (the boiler was installed 2000) - is it the inhibitor? I'm going to put a nail in once I get hold of one (don't laugh!) to see if it rusts compared with one in tap water.

So far, is there anything untoward? Does the clear water indicate that the faulty radiator is OK or can this single radiator be suffering from corrosion?

Next bit. When the boiler was on for ages the cold radiator's 'in' pipe got extremely hot but the 'return' pipe (and most of the radiator) stayed cold. What does this suggest?

Also, I really turned the thermostat up full but found that the boiler would switch off after fifteen minutes. The idea was to see if the faulty radiator would actually heat up eventually. The thermostat is in the kitchen (which is where the boiler is, where the best radiator is and of course the hottest room in the house) - is the thermometer it uses in the same place? Would that explain why the boiler turned off too quickly (i.e. with the faulty radiator in furthest away bedroom still cold)?

I was intending to start opening/closing valves (and ultimately leading to following the 'balancing' instructions) but *all* the valves on every radiator have no covers and they look identical at each end. So, I can't tell if each valve is a thermostatic radiator valve, just an on/off valve, lockshield valve for balancing etc etc! Any ideas how can I make progress?!

Another thing, I am not sure if the central heating is a 'one pipe system'. Does this make any difference w.r.t identifying which valves to fiddle with?

One more question. Quite alot of the valves are a bit corroded/mucky.

From what I've read, it seems that if you are to replace a valve then

the system must be emptied. All the valves could do with replacing but is this that sort of thing 'worth it' - it seems emptying and filling is quite a big proposition?

Oh dear - it's all a bit of a learning curve! Sorry it's so one-sided :-(

Emma

[Roger Mills]

It's very unlikely that you have a corrosion problem.

It tells you that there is only a very small amount of water flowing through this radiator.

The thermostat will respond to the temperature in the room where it is located - unless you have a remote sensor which is sensing the temperature somewhere else (unlikely). So the heating turns off when the kitchen gets hot - even if the other rooms are cold.

If the valves are the *same* both ends, they ain't going to be TRVs (thermostatic). Can you upload a digital of the valves somewhere, and post a reference to it here? If you've effectively got lockshield valves both ends, you can still turn them - it's just that you need a spanner or pliers rather than fingers!

If it was installed in 2000, it ain't going to be a one-pipe system.

You are right that you would have to drain down - or, at any rate, de-pressurise the system - in order to change the valves. They will probably clean up ok with a bit of wire wool followed by metal polish. Personally, I would only replace them if they are leaking, and cannot be fixed by tightening the gland nuts.

It's almost certain that your problem is simply a need to balance the radiators. First find out which is the flow side and return side of each radiator (the flow pipe is hotter). Then fully open the both valves on each rad. Then follow the balancing procedure by progressively turning down the lockshield valves on the return side of the hottest radiators. You'll need to keep the system running while you do this by turning up the room stat to max and, if necessary, opening all the windows.

[emma_middlebrook]

That's good!

This is what I'm a bit confused about. So, first thing, I'll try and open the valve on the flow side of the dodgy radiator to see what happens. That might improve things!

I thought as much! As you say later, I think I'll balance that kitchen radiator somehow so it's on quite 'low'.

This is it!

every radiator has lockshield valves both ends. I hope I don't twist the thing off!

Ah OK! The boiler was a new one installed 2000 but I don't think the central heating pipes were replaced - they may have been done in the

1970s even.

OK, thanks. I'll do the clean up - I really don't want to mess with anything too much.

OK. I'll make a map of the flow and make a start on this.

One thing that mystifies me about all this. If all the flow side valves are open but the 'first' radiator's exit valve is closed how do the others get any hot water?! That's what I couldn't understand about the furthest away cold one - if it's not getting much supply how are the others still getting water circulating around? I've seen a picture of a

2 pipe flow and return system but I still don't quite get it :-(

Emma

[Roger Mills]

The nut with the spanner on *isn't* the bit you turn!! (That holds the valve onto the radiator). The bit to turn is the small vertical brass shaft with a flattened bit at the top. This is what the knob would engage with if you had one.

Assuming it's a 2-pipe system (which it almost certainly is) the radiators are connected in parallel - so the water comes to each one from the boiler without having to pass through any other radiators on the way. So you can turn individual radiators on and off without affecting the others (apart from disturbing the relative flow a bit). Even if it were a one-pipe system, the main flow pipe still by-passes each radiator - so you can turn a rad off without stopping the entire flow.

[emma_middlebrook]

Yep - I know that much but worth mentioning, definitely :-)

I've managed to turn off two radiators so far using a mole grip type thing. One started to leak but I tightened up the nut below the vertical brass shaft a little and it's OK. The other two have rusted solid and am a bit wary of using the same technique. I've got hold of a non-lockshield top that I can fit over but there's no way any of them are shifting by hand.

What I was going to do is turn them all off except the one that doesn't warm up and see what happens - I assume that if the radiator does warm up properly then it is fine. By the way, turning off just two made no discernible difference to the temperature of the bottom of the faulty radiator.

I've also identified each flow pipe and each return pipe. Can I just clarify that turning off the flow pipe will just turn off the radiator and turning 'down' i.e. clockwise the return pipe will allow other radiators in the chain more hot water?

Thanks Roger, for taking the time to explain it, I've got it now. But I still don't understand (if this is actually true) the bit about turning down the valve on the return end (i.e. where the lockshield should be on my radiators) actually helps the others! Aren't they getting hot water anyway because they are connected in parallel along the flow pipe?

Emma

[Roger Mills]

Not exactly! You have a big pipe coming out of the boiler (flow) and another big one going back to the boiler (return). Between those pipes, you have 7 (or whatever) parallel connections - each containing a radiator. Under the influence of the pump, water is trying to get from the flow pipe across to the return pipe. It will take the line of least resistance. You need more water to flow through the big radiators than through the small ones. So you have to throttle the flow through the small ones - which reduces overall flow, causing the pump to increase its pressure - thus increasing the flow through the larger radiators. The lockshield valves are used for throttling the flow - but only adjusted when the other valve is fully open.

If you fully close the valve on the inlet side of a radiator, you stop *all* flow from going through that rad - so that the setting of the lockshield becomes irrelevant. Closing one rad will cause the flow through all the others to increase a bit.

Just to confuse things a bit further, it doesn't *really* matter whether the hand valve is on the flow side and the lockshield on the return side or vice versa. The effect will be the same, and it is conventional to have the lockshield on the return. The important thing is that you use one valve for balancing - and leave it alone once set - and use the other valve to turn the rad on and off completely.

Balancing is simply adjusting the relative resistance of each branch so that an appropriate amount of water flows through it, depending on the size of radiator. If it helps, think of it in terms of a lot of electrical resistors connected in parallel - with more current flowing through those with low resistance than through those with high resistance.

Hopefully this is explained above.

[emma_middlebrook]

Right, I've got one final query. The original post 'no valve tops' actually meant no turnable i.e. non-lockshield tops (this is when I knew less about what was going on). Since then, I've discovered that some radiators have lockshield tops on the inlet and some on the outlets! Given what you've said about it doesn't really matter which side the lockshields go on, it sounds like one must choose one way or another for a *whole set of radiators* otherwise the whole process won't work. Is that right?

I really get it now (minus the mix n match lockshield query above). Thanks for all your help!

Emma

[Roger Mills]

No! Remember that the valves are in *series*. The water flows in through the inlet valve, through the radiator itself, and out through the outlet valve. When adjusting the flow resistance of an individual radiator branch, it doesn't matter where you put the restriction. So some radiators may have lockshields on the flow side and others on the return side - it really doesn't matter. But remember which way round it is for each radiator (unless one valve has a definite lockshield cap and the other one a hand-wheel) so that you don't disturb the balance when you want simply to turn a radiator off. Some radiators - particularly those fed by long pipes which impose a restriction of their own - may need to have their lockshields fully open. This will occur naturally if you do the balancing exercise in the recommended way.

[emma_middlebrook]

OK, I've got it - it took a while :-)

Now, I'm getting a little bogged down but if someone can help then this would be appreciated.

I turned all radiators off except the one that never seems to warm up.

I turned the thermostat to 27C (its maximum) and opened the back door to try and keep it cool.

The radiator did get warmer than it otherwise would except that the boiler doesn't want to come on for more than five minutes or so. I don't really understand this as it certainly won't be 27C at the thermostat so why does the boiler turn off?

Back to the lone radiator. At the top it's the sort of temperature that would be uncomfortable to hold on to. At the bottom centre, it seems just warm. Is this to be expected? Does it actually indicate that I need to investigate this radiator further?

Thanks for listening and helping!

Emma

[Chris Bacon]

Sounds as if it's sludged up. Have it off. Take it outside and flush it out with a hosepipe (with the rad. veritcal, so that the water runs through). Make sure the gunge doesn't get on things you don't want it on.

[Roger Mills]

The boiler turns off because one single radiator cannot dissipate the full boiler heat output - so the boiler will only fire occasionally to make up the heat given out by the radiator. The room thermostat turns the whole lot off when the room is hot (which isn't happening in your case) but the boiler has its own stat to control the temperature of the output water - and it's this which is cycling.

Sounds like sludge. It builds up in a triangle at the bottom - so the centre part is cool quite high up, but it gets warmer as you move away from the centre. Is this what you've got?

If so, it will need to be removed and flushed out, and you need to check - and probably replenish or replace - the corrosion inhibitor in the system.

[emma_middlebrook]

Ah, cheers!

There's now a twist. I just turned the hot water on upstairs in the kitchen (where the boiler is). There was no hot water. I left it like that for five minutes to see what was going on because the boiler had definitely switched on. Just on the off chance, I happened to go down to the room with the radiator that's the only one currently on and the whole thing is boiling hot! Even the bits that weren't getting hot before.

What the hell does this mean?!

To be honest, I'm getting really tired of all this house stuff because it just seems endless (I've got enough questions on everything to fill about twenty separate threads) :-(

Emma

[Roger Mills]

It means either:

1. It wasn't sludge - but you just hadn't left the radiator long enough to warm up previously, or
2. It *was* sludge - but putting the full flow through one radiator has washed it out, and re-distributed it around the system