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Leon

Hi,
When my central heating has been on for a bit the central heating header tank overflow is dripping about one drip every second or two. Not such a problem at the moment but it wasn't doing this a month ago so I guess something has gone wrong.

I have an old Vulcan Gas boiler. The water pump was replaced some years ago. There are two settings on the boiler controller. Hot water only (This actually heats the hot water and also the upstairs radiators at the same time. Always has done) and hot water and heating. This heats the hot water and all the radiators in the house. The hot water is stored in an emersion tank that I can also heat using electric. If I turn the emersion tank on to heat the hot water I don't have a problem. It heats the hot water as it should and nothing else.

When I first noticed the dripping I went into the loft and noticed that the header tank was full of warm water. Pretty warm but not boiling hot. The water was also 3/4 up the ball cock float. I have changed the ball cock and float with a new one. I have also cleaned out the header tank and let it refill. Now when I turn the heating on I can see water coming back into the header tank from the exit pipe at the bottom of the tank. I am not sure if this is normal? It seems to be warm water that is coming back in too.

I have tried turning the pump down from 2 to 1 - no difference. The only thing I have done on the system in the last 2 months is replaced 3 radiators in downstairs rooms with new ones. I am sure that is just a coincidence though.

The hot water and the radiator water isn't mixing. I have run a bath of hot water and it is fine.

Is the water coming back into the header tank normal? Any thoughts as to why I am getting hot water in the header tank and a steady dripping in the overflow when the heating is on?

Thanks
Leon
 
It depends.

If you have a small header tank, (around 10 gallon), for the Heating which is separate to the cold water storage tank, then that would normally be a Feed and Expansion tank.

It is there to initially fill the Heating system and to top it up when you bleed a radiator or loose water for another reason, such as a leak, for example.

That tank is also there to take up the the expanding water in your Heating system.
The water in your Heating system can expand 1/23 by volume whilst being heated.
So for example, if your Heating system contains 23 Gallon, you would have or expect up to 1 gallon of expansion (Volume).
There will be a flow of expanding water into your F+E (feed and expansion) tank but the level in that tank when cold should be low enough so that the water level does not rise too far. You would also not really notice a quick change in the level as the water expands. I would think if it's an old system, that extra volume should take around 30-60 minutes to appear.

(rules of thumb, my experiences, my opinions here you understand, plus I haven't seen it).

Just so I don't write War and Peace:-
How far would you say the level rises?
How fast does it rise?
What is the level in the tank when the Heating system is cold?

Could it be possible that the Ball cock was passing and you changed it but didn't set the level low enough with the new one?
If it's a part one brass valve, you bend them to set the depth.

The cold level in that tank would normally be 4"-5" ish, I would say a couple of inches above the outlet and check it when the pump is running too.

The cause of your upstairs radiators working when Hot water only is on is Gravity circulation or at least I suspect it is. You could have an anti Gravity, (single check valve), fitted to the heating circuit, which would mean the Heating only comes on with the Pump. This is of course something you need a Heating Engineer to look over for you as it needs someones eyes on the job first, for safety reasons.
 
Thanks for the reply. Yes, lets ignore the upstairs radiators heating up. I only mentioned that to explain the system. That is fine for me. In the attic there are 3 tanks. Two large ones and this smaller one. About 40cm x 30cm and about 30cm deep. I will adjust the ball cock so it isn't so deep. At the moment it fills to within about 4 or 5 cm of the overflow (maybe a bit more). I will run it for a few hours and see what happens. Thanks again.
 
No Problem at all.
You could turn the water off and bale it out of course to save time and then set it as it should be.
When running there should be no water pumping over the expansion either.

This Boiler, is it a Vulcan Continental ?
Don't see many now, nearly all gone. It must be over 40?
 
I did turn the water off and bale it all out.
It is a pretty old boiler. Simple though and as long as I don't forget to change the thermocouple every year before winter it runs like a dream (ish) :)

It is usual for that tank to have warm water in it when the heating has been on for some time? Seems like a terrible waste!
 
I did turn the water off and bale it all out.
It is a pretty old boiler. Simple though and as long as I don't forget to change the thermocouple every year before winter it runs like a dream (ish) :)

It is usual for that tank to have warm water in it when the heating has been on for some time? Seems like a terrible waste!

They can be warm after the water expands into it but they wouldn't normally stay warm for long.

You are supposed to be Gas Safe registered to work on Gas Boilers you know?
(thermocouple).

There are hidden dangers in that Boiler too. Unless they've been changed in the past, the seals will be asbestos.
 
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