cold water tank over flow pipe

[lognak]

Hello,

I have recently had the 3 way valve fixed (due to the wiring set up). I now have hot water available from the gas whereas before I only had HW&CH together. This work fine now.

The problem is when I run the hot water off the gas in the mornings the cold water over flow pipe starts to drip outside (fast drip). It does it at no other time apart from when the hot water is put on.
The last couple of mornings I have been running some water to empty the tank a bit and on refill it doesn't over flow.

Does anyone have any ideas as what's going on. Why would the cold tank overflow only be happening shortly after the HW comes on and no other time? I can't spot what's happening.

Many thanks,

 

[doitall]

Sounds like a backflow, or someones piped it up wrong.

What boiler and cylinder is it.

Have you checked to see whether the header tank or the storage tank is overflowing.

 

[cantaloup63]

Doesn't sound entirely dis-similar from this.