Overflow constantly dripping

We originally had problems with the boiler locking out, a new board in the Potterson boiler sorted this and we have had Hotwater and heating fine.

However i have just noticed that the overflow from the top tank is overflowing outside pretty much constantly. This seems to be more of a problem when the boiler is heating the water, when the pipe is more the dripping. The water is Hot as i can see the steam coming off it.

Ive noticed the expansion pipe is dumping Hot water into the top tank when the boiler is running which is increasing the level.

Any ideas of anything i should have a look at?

Thanks in advanced.

Jon

It would appear that the ball valve inside the system was properly shutting the valve off so water is constantly being topped up.

We just got our bill for a month and its £120 Gas, we only use the heating twice a day for a total of about 4 hours.. Im dreading what our water bill is going to be..

Hi given the last response can you please tell me how you resolved the problem??
My header has exactly the same problem however (i) I can't adjust the current float valve as it is so furred up there little visible metal/plastic (ii) I have removed it from the side of the tank however, cannot get it out the top of the header in order to clean/adjust/replace.....grrrr!!
Any help or advice on this matter would be greatly recieved ;}
thanks

Hello,

The pipe which connectes to the ball valve had a stop valve on it outside the tank. I used a flat blade screw driver to just stop the flow of water as the water level should never change in the expansion tank.