Tank overflow dripping

[No_idea]

Firstly, please excuse my ignorance on this topic - any pointers would be much appreciated.
My loft contains a cold water storage tank which I understand feeds hot water supply in house via cistern and pump. The overflow has recently started dripping quite steadily. I've checked the tank and the ball cock seems to be working as no water is being added to the tank by this means.
I presume it is possible that the tank is back filling somehow through the water outlet on the tank?? Is this possible? And how could this be resolved?
Thanks

 

[onceceltic]

I am no expert however, Had a similar issue to this. Have you got a thermostatic shower.

In my case the non return valve on the cold water feed was not shutting off fully and due to the higher pressure was pushing water back up the hot water pipes to the storage tank.

Changing the valve sorted the problem

 

[josh]

I am no expert however, Had a similar issue to this. Have you got a thermostatic shower.

In my case the non return valve on the cold water feed was not shutting off fully and due to the higher pressure was pushing water back up the hot water pipes to the storage tank.

Changing the valve sorted the problem

That would only happen though if you had no equal pressures on the shower (cold main and the open vented hot) and with that the shower wouldnt work properly.
Are you sure the ball valve is deffintly shutting of fully?
Do you have a smaller tank and if so is it higher than the bigger one?

 

[PETE 123]

Water could be leaking in cylinder coil if its got a cylinder in you system.either by the small header tank or if you have a sealed system.

 

[No_idea]

Thank you all for replies. I have checked the ball valve and definitely not a problem with this. I only have one tank which is in the loft.
The hot water is pumped around the house but not sure whether this is at all relevant?
the shower once turner on is very low pressure and I need to alternate between bath and shower flow on the unit until the high pressure kicks in. Either this or flushing the toilet actually helps the hot water kick into full pressure. Again, not sure whether this is connected to the original problem but someone has suggested that I clean and possibly replace the non return valve on the hot supply of the shower valve.