Central Heating Feed Tank Overflowing

[AL-min]

Hi all

My central heating feed tank (small tank) has recently started to overflow out of the pipe shortly after the heating starts up.

I have only been in the house for a year so im not over familier with the system, but I do know its a vented system with a gas back boiler

I first suspected the ballcock/valve but this apears to be shutting off and I have set the ballcock at different levels to try and over come the problem, but it make no difference where ever it is set, infact if its set low then the water rises over the ballcock and straight out of the overflow.

There seems no water coming from the "vent pipe" to cause this I am begining to suspect that the extra water is coming back up the feed pipe as I can see a haze in the water due to temprature differences

Can this be the case and where could this extra water coming from? And how would I go about resolving it???

thanks in advance

Al

BTW. The central heating seems to be in good working order apart from this.

 

[ChrisR]

Is your main cold water cistern's level above the ch one? If so it's most likely your hot water cylinder is leaking between the two. New Cylinder required.
It would do it all the time but of course the water volume in the CH system increases when the boiler starts, through expansion.

 

[felix]

ChrisR might be right about the leak but I think there is a simpler explanation. As he also says, water expands as it heats - that's why it's called an expansion tank - but air expands many times more. Try bleeding your radiators.

If you want further confirmation that this is a simple expansion/contraction problem - and if you have the patience - watch the tank level fall as the system cools down. Does the ball valve open to make up what you lost down the overflow?

 

[AL-min]

Thanks guys

Yes the feed tank head height is lower than cold water tank

Ok I'll check and bleed the system and keep an eye on the ball valve before I take drastic measures like ripping the cylinder out Although my radiators are all getting hot to the top

I'll let you know how I get on

Thanks again

Al

 

[bobb]

Hi all

There seems no water coming from the "vent pipe" to cause this I am begining to suspect that the extra water is coming back up the feed pipe as I can see a haze in the water due to temprature differences

I had the same problem and it was a hot/ cold mixer letting by with cold mains pressure against hot water from a vented cylinder. The cold water pushed hot water into my cold water tank and caused an overflow. I also saw the haze caused by the hot water. Cured by putting non return in hot pipe to mixer.

 

[croydoncorgi]

Overflowing F&E CANNOT be caused by faults in taps, etc, UNLESS there's ALSO a problem with the heating coil in the hot water cylinder.

Given that in this case the water level in the cold tank is higher than the level in the F&E, and the F&E is being back-fed with warm water, it's a racing certainty theres a break in the coil.

 

[bobb]

you're right coydon. i hang my head in shame. didn't read the question properly. F&E tank, not the cold water tank.

Tch! Bloody amateurs!

 

[felix]

With the cold tank being above the boiler's header tank, a leaking cylinder coil will have that header tank overflowing even if the heating system is switched right off, ie no boiler and no pump. Unfortunately, this isn't the best time of year to do such a test!

 

[gasman1234567892001]

its not hard to explain jus pipe your feed pipe to the expancion pipe and prob solved. it is not piped up right. thats all. its comming back througe the feed pipe and expanding. if it was the cylinder the expantion tank would be filling all the time with water

 

[doitall]

its not hard to explain jus pipe your feed pipe to the expancion pipe and prob solved. it is not piped up right. thats all. its comming back througe the feed pipe and expanding. if it was the cylinder the expantion tank would be filling all the time with water

Rubbish.

cold feed blocked followed by a new cylinder

 

[Frinks]

Hey chaps!

Got the same problem! Overflowing from the F&E tank... boiler on or off!

definitely a leak in the coil cos of the following...

return piping from the indirect cylinder to the boiler was replaced recently on (advice by yes! British Gas Engineers) and when reconnecting found clear water trickling from return outlet. Ohh the heating system was drained totally so it was bone dry.

Is replacing the cylinder a tricky job? I have done loads of pipework in the past but not a replacement tank. Are there regs?

Cheers fellas n galls!