water tank overflow

Hi
My water tank is over flowing for past few days intermittanly
This is been fixed few months back in last winter end by changing the valve which stops it over filling

Is this anything to do with central heating?
(I thing this is from cold tank because the flow is full)

What could have been caused this?

Is there any where I can find detailed information correcting this?

Will this be covered by Emergency breakdown?

There's more than one possible cause, and it can sometimes be an obscure problem.

Can you shut off the supply to the cistern without affecting the rest of the house?

If so, then do it, and see if the cistern still overflows. If it doesn't then you might have a faulty float valve, but if it does then you need to look elsewhere, for example a mixer valve that has unbalanced supplies.

Hi
Thanks
I am new to lot of terms in heating
Can you explain me what's CISTERN
if you are mentioning the inlet from the street then
i haven't tried
but i did tried closing the valve under wash basin in kitchen where the main water is coming from out of house which temporarly gives relief.

this also happening if i fully open the main inlet valve or when central heating or hot water is on.

any ideas???