radiator not getting hot at bottom

Can anyone help please. My neighbours radiator in the bedroom is getting hot at top, but not the bottom. It is a puzzle to me why. Any suggestions? Thanks Neil

Reply to
Neil
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If the outlet is cold, then the flow is too small. If the outlet is hot, then the radiator is silted up.

Reply to
Andrew Gabriel

This one is a classic.

Basically the system has accumulated sludge consisting of iron compounds from corrosion of metal components - principally the radiators.

Inside the radiators, the flow speed past any given point is fairly slow, whereas in the pipes it is faster. Hence, the sludge is circulated and deposited typically in a triangular pile at the bottom of some or all radiators. Thus, heating water doesn't reach these areas and they feel cool. You can easily feel the shape and size of the pile in each.

All of this comes about through a combination of

- possible poor system design where the pump causes water to be pumped over the header tank vent into the tank or it is sucked down instead, thus introducing fresh oxygen and promoting corrosion

- lack of a corrosion inhibitor added to the system normally annually.

Eventually, the radiators will deteriorate to the point of developing holes and leaking.

The fix is to thoroughly drain and clean the system.

This can be done by draining completely and then taking the radiators off and outside one by one. Containers to catch the water and sludge and plastic bags rubber banded onto the disconnected radiator tails are important since sludge is an indellible stain on furnishings. Once outside, they should be thoroughly flushed with a pressure washer ot mains water hose.

The system should be flushed at each radiator position such that anything in pipes is delivered out as well.

After this, the system can be reassembled and at that point it is a good idea to add a flushing agent. THis is a chemioal additive which is run hot in the system normally for a week. It will pick up and dissolve a lot of remaining material. After this, the system should be drained and thoroughly flushed again and finally a corrosion inhibitor added.

An alternative approach is to do powerflushing. This can be bought as a service - BG love to do this and relieve customers of £500-800 for the privilege. One can rent the equipment and buy the chemicals from tool and equipment rental places for considerably less. This technique works by pumping a chemical solution around under pressure and forcing the sludge through. Efficacy may vary.

Reply to
Andy Hall

Thanks for the advice. With it been one radiator do you think taking that one of and flushing it out may solve the problem? I am a bit reluctant to attempt the whole system for them. Neil

Reply to
Neil

An accumulation of sludge at the bottom of the radiator. Remove the radiator, take it outside and flush it through with a hosepipe. That should do the trick.

You may wish to consider adding extra inhibitor to the expansion tank before refilling though.

Reply to
Dark Angel

Do note Andrew Gabriel's point as well though. One radiator *can" be cold at the bottom due to very low flow because the lockshield or radiator valve (or both) are set too low in comparison with others. This would manifest itself as warmth up the end of the radiator where the flow enters, warm across the top and then cool towards the bottom and return side.

If it turns out to be this, then try adjusting open the radiator valves on that radiator. If that doesn't work, then you can try the balancing procedure in the FAQ, which will involve reducing the flow through other radiators to divert more water through the misbehaving one. I'll warn you that this is a time consuming procedure, though.

However..... If it turns out to be sludge (telltale "pile" in the bottom), then I suspect that you will find two things.

1) If you feel all the radiators shortly after the system comes on, you will probably find sludge to some degree in all in the form of a cool area. If there isn't too much, the radiator warms eventually by conduction through the steel. 2) When you drain the system, the water will be filthy black.

If you have the first scenario, then just flushing the bad one will eventually mean that there will be some further build up and you have to do it again.

So really it is better to do it properly if possible.

Another short cut is to just do the one radiator and then use the flushing agent in an attempt to deal with the rest. A bit unpredictable, though.

One thing that is important is to make sure that there is no pumping over or sucking down in the feed tank. Go up into the loft and ask the neighbour to start and stop the pump on the heating by turning the CH off and on. You are lookig for dribbling out of the vent pipe or listening for a gurgling sound. Make sure that there is about 75-100 mm of water in the bottom of the tank. It should comfortably cover the feed pipe exit when the system is cold and not approach the overflow when hot. If water overflows then it gets replaced by fresh and this becomes another cause of corrosion. Adjust the float valve if you need to do so.

If pumping over or sucking down is suspected, try to trace where the feed pipe from the tank and the vent pipe join the main circuit. They should connect no more than 150mm apart and should definitely not be on opposite sides of the pump. If this bit is wrong it becomes a plumbing job. You can cheat by reducing the pump setting sometimes but often that results in inadequate flow to the radiators.

However, it is very important to fix this problem if present or the corrosion will continue.

The other essential part at the end is to add corrosion inhibitor, but there is no point unless the system is already pretty clean.

Above all, so make sure that you protect the neighbour's decorations and furnishings by having copious amounts of plastic sheet, old newspapers and towels etc. THe water will stain and it will not come out. For containers under the ends of the radiator, new cat litter trays from the supermarket work well.

Good luck.

Reply to
Andy Hall

Thanks to Andrew, Andy and Dark angel for help and advice. I am going to give it a go this morning. Neil

Reply to
Neil

Great. Do please come back with the outcome.

Reply to
Andy Hall

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