One radiator always needs bleeding

20 y/o Bungalow, 20 y/o original oil fired boiler, 10 rads of which only 3 are used (kitchen/diner, shower room and my bedroom). The rest of the house I rarely even go into so no point heating it. The shower room rad is the closest to the boiler and the first to heat up. It's needs bleeding every couple of weeks. Yesterday it was almost full of air - just the bottom rail heating up. The other two never have any air in. There are no zone valves for the heating so the water has to run round the whole house to get to the three rads I do use. Just for Fiesta XR2i's and giggles and to double check I'm not spikkin bollocks I've gone round the other 7 rads today which have never been looked at for two and a half years and not a trace of air in any of them after all that time.
There are no leaks from that rad, or any other as far as I can tell, or the boiler but what goes on under the floorboards in the sump under the house where the pipes run is anyone's guess.
Suggestions as to why air gets into just that one radiator? If the leak was elsewhere, like under the floor or at the boiler then surely the pipework would carry at least some of it to the other rads?
If it's a corrosion gas issue then it's vanishingly unlikely to just affect one rad methinks.
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Quick update. Right after posting the above while having a shufti round I spotted a pipe stub and bleed nipple coming out of the boiler itself. There was a good bit of air in that too.
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20 y/o Bungalow, 20 y/o original oil fired boiler, 10 rads of which only 3

I also have to bleed by shower room towel rail more far more often than any other rad, but not to the degree you are doing. I have always put it down to the fact that it is taller and mounted higher than any of the radiators.
Mike
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On 26/01/2015 11:34, Dave Baker wrote:

When was the last time your system was drained, or had any inhibitor added to it?
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Air that's got dissolved in the water will always come out in the boiler. You tend to find that bubbles coming out of the boiler do always end up in the same radiator (not necessarily nearest the boiler), due to the pipework layout.
What sort of system is it, vented with a small loft header tank, or sealed with a pressure guage and filling loop or valve?
Do you know if it has inhibitor and how long it's been in there?
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It does tend to collect at generally the highest point. Assuming it is air - and not the product of corrosion - there must be a leak somewhere. It may well only happen when the water is hot and if minor difficult to find due to it evaporating quickly.
If you can think of a method of pressurizing the system cold, could be easier to find. If you have thermostatic valves I'd look at those first - remove the thermostatic part so you can see the actual valve.
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That's interesting. Thank you.

The former.

That's a question I'd love to ask the previous owner and have been intending to do. I've only been here since May 2012 so I don't know the history but given the age of the bungalow (early 90s) I doubt if it's been touched since new. Regardless I think it might be prudent to flush and refill with inhibitor in the summer when it's all swiched off. I stupidly allowed the system in my old house to corrode out due to no inhibitor and am determined to not let that happen again.
As a subsidiary question is it practical to flush the rads in situ without a pressure flushing rig just by draining/refilling/draining a few times?
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On 26/01/2015 12:18, Dave Baker wrote:

Well, you've left it nearly 3 years already! Time to get on with it!
It might be worth checking what actually comes out of the radiator, first. When you next bleed it, stick a lighted match to the 'air' coming out and see whether it burns. If it does, it's almost certainly hydrogen - resulting from corrosion - so adding inhibitor is urgent. If it doesn't, check the fill and expansion tank carefully to see whether the system is pumping over. If water is flowing out of the vent pipe, back into the tank, this is *bad* and will almost certainly introduce air into the system - quite apart from wasting energy and causing condensation in the loft.

Not really. Best to remove each rad in turn, take it outside and flash it out thoroughly with a hose pipe. [Be careful not to spill any black gunge on the carpets as you carry it out. Best to stuff a bit of kitchen roll into each each tail.] While each rad is off, open each of its valves in turn in order to flush out the pipework.
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And? This is uk.d-i-y:-)
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On 26/01/2015 12:18, Dave Baker wrote:

Make sure that you are not over pumping and cycling aerated water around the header tank.
I've found that filling/emptying the system a few times alone does little to get the sludge from the radiators.
Try also fitting an auto-bleed valve to the problem radiator.
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On 26/01/2015 12:18, Dave Baker wrote:

Its fairly easy to do on sealed systems, but not quite as easy to do effectively on vented ones. Although if you temporarily cap of the feed and vent connections to the header tank, then you can mains pressure flush it like a sealed one. See
http://wiki.diyfaq.org.uk/index.php?title ntral_heating_flushing
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On Mon, 26 Jan 2015 11:34:54 -0000, Dave Baker wrote:

But for some reason gas frequently only ever accumulates in the rad nearest the boiler. Presumably because hot water can't hold as much disolved gas as cooler.
Does the expansion tank get warm/hot, is the pump over. May only be a little dribble when the pump starts or stops but that is enough to introduce airated water into the system.
The system does have inhibitor in it doesn't it? Can you remember when it was last topped up? If it's a long time, just bung another bottle. Pretty sure you can't "overdose".
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A flush would be prudent if the inhibitor is old or non-existent. For a sys tem not badly sludged up then chemical cleaners will do the trick. Running water through will help but will not tend to flush out badly sludged radiat ors. The best method I have found is to remove individual radiators outside and run the hose or use a high pressure machine to remove the sludge. It's a mucky job but if you have the time and the radiators are easy to drain a nd remove then it really makes a difference. Power flushing by professional s can costs hundreds and I am not convinced it does a better job than I hav e described above.
Richard
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wrote:

When I moved into this house in 1998 all of the radiators needed bleeding, then after that only a small one at the top of the stairs, near the airing cupboard, needed bleeding, probably once a year. I installed an automatic bleeding valve in that one and none of them have needed doing since. (http://www.ebay.co.uk/itm/GENUINE-HV30-Automatic-Aladdin-Valve-Self-Bleeding-Radiator-Valve-/171542307976 , search eBay for 171542307976 if the link is mangled.)
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For the sake of 15 quid, I would buy a bottle and pour it in the header tank now, even if you end up draining it all off in the summer. Even if it was put in just before you moved in, 3 years is probably pushing it for a vented system. (In a sealed system that doesn't need topping up, it can last much longer.)
While you are up there, when the heating is on, check that hot water isn't running from the vent pipe back into the small header tank (if it has a vent pipe looped over the top, which most but not all do). Ideally, do this when the thermostat is calling for heat, but any TRV's you have will be closing because those rooms are are up temperature. Depending on system design, this is often the situation where pumping over is most likely. Also check the tank isn't hot (perfectly OK if it is slightly warm, as it's heating and expansion of the water in the system which pushes the excess up into that tank, but it shouldn't be at radiator temperature as that would also indicate it is pumping over).

Yes, unless they are sludged up. You can easily check for this by feeling the bottom of a radiator when the system is running and is all up to temperature. For each radiator, check the inlet and outlet pipes are hot indicating there is flow through it. Then feel the bottom of the radiator around the middle. This is where sludge collects and it will be cold (or noticably cooler than the inlet and outlet pipes) if there's a build up of sludge there.
The other thing that helps flushing is to force the flushing water through each radiator one at a time. Do this by fully opening all the lockshield values, and with the pump running, turning off all the radiators except one at a time. You will either need to rebalance the system afterwards, or before opening the lockshield valves, count the number of turns to fully close each one and record this, setting it back to the same position afterwards. You need to record this in fractions of a turn, as some may only be opened a quarter of a turn, or even less for a small radiator near the boiler. Opening all the lockshield valves also serves to release any debris caught in them, as they are often the narrowest openings in the water paths in a system.
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Andrew Gabriel
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All excellent advice, thank you. The rads feel good at the bottom centre but nonetheless I think when the warmer weather comes around I'll give the whole system a going over and depending on what colour the water is that comes out of the drain cock I might take each rad out and give it a good blast through with the pressure washer.
My lack of TLC with the system in my last house for 20 years, ignoring the black crap that came out every time I had to drain it to fix a leak and never using inhibitor because there was always just "one more job to do" before I could call the system finished resulted in a decidedly moist lounge carpet which I traced back to a 2 foot jet of water spraying horizontally out of a pinhole in a completely rusted through rad onto the back of the cupboard it was hidden behind followed shortly after by the boiler heat exchanger cracking due to it being half full of rusty sludge. I managed without heating for the last few years until I sold it as a do'er upper but that bottle of Fernox I never put in probably cost me several thousand quid plus a thoroughly miserable cold existence every winter managing on gas and electric fires. I ain't going there again. Penny wise - pound foolish.
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On 26/01/2015 17:29, Dave Baker wrote:

It's best to add the inhibitor to the towel rad, as they usually have removable plugs at the top, so shut the rad off (both valves!) bleed it until no more water comes out, then remove one of the plugs, syphon some water out into the handy nearby bath/basin/loo! and then funnel the inhibitor in.
If you add it to the expansion tank, it may end up mostly staying up there rather than getting around the system immediately.
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Have you checked it's not pumping over? If you've shut down some rads, it's more likely.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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You might find air is being sucked down the expansion pipe by the pump if the system is not correctly designed. (This is the pipe that curls over the top of the header tank.) Also check that there is sufficient water in the header tank , it needs to be around one third to a quarter full. Stopping this might be as simple as reducing the pump speed (switch on pump.)
If already running at minimum speed, try throttling the pump using one of the isolator valves. This is a temporary solution only, there will need to be a permanent fix.
This is a quite likely one as it's made worse by turning most off the radiators off as you have done making the pump "too big" for the remaining system.
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