CH header tank overflowing

[MJT]

My central heating system is just over 30 years old and was installed when the house was built. From day one we have always had air building up in one of the radiators on the hot water cylinder convection part of the boiler system, there are two radiators on this circuit but always the same one collected air. The builders plumber returned a number of times but only checked that the air was not a flammable gas and put inhibitor into the CH header tank, and then refused to answer any further calls. So we have just lived with the fact that I had to bleed the radiator every month or so.

The system has been drained down a number of times over the years to repair leaks, change radiators and move the boiler to a new position.

Recently we changed the radiator that collected air from one which was 1800mm wide x 600mm high to a modern upright model which is 600mm wide and 1600mm high, and since then no air has collected in the new or the other radiator on the circuit.

What happens now is that water is being fed into the CH header tank, through the overflow pipe, which then overflows. I think this is because the top of the new radiator is higher than the top of the hot water cylinder and so the old problem of air in the system is still with me but is now in the feed to the cylinder coil. The cylinder was replaced about 5/8 years ago after advice from DIYnot.

Is there some automatic way of removing the air?

 

[stardanny]

Did you make sure the Ballvalve for header tank isn't letting by and does the overflow to outside always run regardless of heating on or off?

Daniel.

 

[MJT]

No the overflow is not always running, it's only after I have been running the boiler for a day or two.

Regards,

Jim

 

[ChrisR]

water is being fed into the CH header tank, through the overflow pipe, which then overflows.

You probably meant the VENT not the overflow - it can't fill via the overflow.
If you mean there's no water entering via the ballcock then your HW coil is probably perforated, so it's letting cold water through, assuming the water level inthe CW cistern is higher than that of the CH cistern.
Water is coming out of the VENT because all that air going round has caused sludge to build up where the FEED pipe is Teed in to the circuit. That's probably just after the vent so the pump sends water up the vent. Common as muck....
You wouldn't use aggressive desludge chems on a system that old so you meed to remove the pipes, to clear the T out.

Your air could be getting sucked IN on the input side of the pump, without it letting water out. Also fairly common, though it usually looks like it has leaked at some point - eg green..

 

[ChrisR]

The cylinder was replaced about 5/8 years ago after advice from DIYnot.

Same problem has returned then - same cause! Corrosion! Air means o2!

 

[MJT]

ChrisR,

You are correct, it was the vent pipe I was referring to. The cylinder was changed because I could not get the failed immersion heater out to replace it after many attempts by various methods.

The air problem has been with me since the day I bought the house and has stayed with me irrespective of any changes made to the system.

This problem has only occurred since I fitted the taller radiator, do you still think it is a leaking cylinder coil?

Regards,

Jim

 

[75pete]

My guess would be, part blockage of the fill. This could be due to some muck that was sitting in the tank then being drawn down when the new rad was fitted, thus part blocking the fill and leading to your problem.

 

[ChrisR]

This problem has only occurred since I fitted the taller radiator, do you still think it is a leaking cylinder coil?

Water doesn't know anything. Nor does air. Air in the top of a rad isn't connested to air anywhere else. It doesn't decide to go down then along to see if there's any rad which is higher.
Air also does not make water materialise ina circuit. If water is coming out, then it's going in, somewhere. Turn off your inlet just to be sure - or tie up the ballcock if there's no stopcock.


Water barely moves in the feed pipe, it goes up and down as the water expands and contracts, that's all. No "part blockage of the fill." is going to seal it, and even if it did, so what? If you put your arm into a heating F & E tank and plug the outlet , it's not going to make water come out of the vent.
Blockages happen all by themselves where I said - in the circuit where the tee from the feed meets the circuit. I think I drew a picture for a FAQ here a few years ago. Often you get a 6mm hole through the middle of hardened scale. You may have disturbed it. Cut the pipes out and have a look. That won't cure your gaining-water problem though.


here - 7 years ago
//www.diynot.com/diy/threads/faqs.37170/#post-891831

 

[MJT]

75Pete said"You can get Autovents to replace bleed points in the rad and pipes."

Could you tell me where I should fit the autovent i.e.higher than the cylinder or just above where the hot water enters the cylinder coil.

For all those helping I would point out that the hot water system is not pumped, only the central heating radiators are on a pumped circuit.

 

[Agile]

How do you expect the tall radiator to fill with water to the top if its above the level in the F&E tank?

Tony

 

[MJT]

Tony,

The tall radiator's top is higher than the hot water cylinder, but is not higher than the feed tank which is in the loft.