Central Heating Header Tank Overflowing

[markpearson]

I have a open central heating system and when i turn the heating on it's fine. But when i turn the hot water on it starts to over flow from the header tank ( the small one). It's not a fast flow of water but more then a drip! What could be happining and what can i do to fix it?

Many thanks Mark

 

[D_Hailsham]

Do you mean that water is coming out of the overflow which exits the house under the eaves?

Or do you mean that water is coming out of the pipe which hangs over the small tank?

 

[markpearson]

It exits the house through the over flow pipe. I had a look at the Ball valve and that isn't leaking or damaged, it's just when the hot water is on! Any ideas?

 

[D_Hailsham]

It exits the house through the over flow pipe. I had a look at the Ball valve and that isn't leaking or damaged, it's just when the hot water is on! Any ideas?

How deep is the water when the system is cold?

It shouldn't be more than an inch or two about the lower outlet to the heating system. The important thing is that the ball valve opens just before the water level reaches the outlet, This prevents air entering the system.

If the level is too high, bend the arm of the ball valve to lower the level.

Have you checked if any water is coming out of the vent pipe which hangs over the tank?

 

[markpearson]

Firstly sorry for the delay,

I have just turned my hot water on and it has started to over flow out of the house. I went into the loft to check weather it is coming out of the ball valve or from the over flow from the tank.
Well it doesn't seem to be coming from any of them but on closer inspection it looks like the water is heating up and expanding from the tank and into the loft, were it is only then it seems to be over flowing out the house. I felt the water and it is warm! Is this how it is supposed to work and why would it do this? I hope you understand the problem and hope i have highlighted the points needed to pick your brain.

Hope to hear from anyone soon as this is feeling like a bigger problem then i originally thought.

Thanks

 

[SteNova]

we used to have this issue when we were coal fired, when very windy it would force the water to boil, lots of steam and water overflowing from the header tank, the only way to stop it was run the heating pump and open the hot taps to loose some of the heat

if your water level is rising you must have some water that is too hot somewhere, as the water doesn't expand till 100 deg?

may be unrelated and not right in your case but wasn't there a case a few months ago in the news where a hot tank boiled over dumped into a plastic tank that melted the killed a baby?

http://www.guardian.co.uk/uk/2008/jan/08/uknews4.mainsection

 

[Boilerman2]

Who told you that water dosn't expand untill 100'c what a load of tosh! Water expands from the moment its temperature starts to rise!! at 100'c something amazing happens....IT TURNS TO STEAM!! may I respectfully ask that you don't offer advice unless you are absolutely certain that the advice is credible??

 

[SteNova]

thats why i put a ? after it what percetages does it expand by??

just looked

1% at 50deg
4.4% at 99deg

so what is the volume of his heating system and what temp does it run at

and the size of the tank and the cold height and the overflow height

 

[SteNova]

Water expands from the moment its temperature starts to rise!!

and no it doesn't it starts to expand from 3.98 deg

 

[robin7]

motorised valve failure, perhaps?

 

[markpearson]

Thanks for the reply lads.

just to put something out there, i have been reading up on heating systems and the FAQ on this site and someone said about the coil in the tank having a hole in it. As one of you said if water is too hot somewhere else ( like the heating side ) and there was a hole in the coil would that make the level rise? Also i know for a fact the immersion heating element in the tank is bust because it keeps tripping the fuse box, could this have a factor in the problem?

Hopefully your not all bored yet of my problem as i'm greatfull for the input!

chears

 

[markpearson]

Sorry but what is a motorised valve (it's not the 2/3 port valve, is it)? where could i find it? and how do i know it is faulty?

 

[Hugh Jaleak]

I doubt this will have anything to do with a motorised valve.... Holed coil would cause an overflowing F&E tank, but this would probably be a constant overflow. Still need an answer to D.Hailshams question about the level in the F&E tank. System cold the water should be a few inches above the outlet, well below the overflow pipe outlet.

If the tank is virtually full when the system is cold, then the slight expansion when boiler is working will cause it to overflow. Then as the water volume decreases as it cools, the ballvalve will top it up again, and next time the system heats up it will overflow again...

Motorised valve is the 2/3 port valve, if faulty it wont cause this problem, failure usually means either heating or hot water doesnt work when required. If the immersion is tripping when you switch it on its likely goosed, wont work and needs replacing! Again, will have nothing to do with this issue.

 

[markpearson]

I have checked the level of the water when the system is cold and it is only a couple of mm below the overflow outlet!

would that mean there is too much water in the system before it starts to heat up, if thats the case what would be solution to stop it filling up so much?

cheers

 

[Hugh Jaleak]

Yes, level is too high! So long as there's a couple of inches above the outlet when cold thats all you need. Either adjust ballcock so level is lower when it shuts off, or replace it if it keeps dripping! Drain some water off to lower level in F+E cistern.