Expansion flowing into header tank

7 Sep 2007
Reaction score
United Kingdom
Asking for a friend. This morning, they noticed a constant flow from an overflow. On investigation, it appears that is it from the CH header tank from their description. (Small tank, ball cock inlet, bottom outlet, overflow and open pipe curved over the top of the tank presumably the expansion pipe) There is a constant flow coming from the expansion pipe into the tank. As they are certain that their CH pump is off when the CH and HW are off (which it is) I suggested that they turn a hot tap on to see if this affects the outflow. It does. With a hot tap on, the outflow reduces to zero, when turned off it comes back.

To my mind, this sound like there is a hole in their coil within the hot tank that is allowing water to go into the CH/HW boiler circuit which is overflowing into the header tank. Aparently the HW tank is about 20 years old. Any other thoughts?

Update: the HW tank is an Ariston STI210 Unvented cylinder.
Last edited:
Sponsored Links

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local