Overflow from expansion tank while hearing is on

Hedgecutter

There is a small amount of water flowing from my expansion tank when my heating is running. It's oil burner system with 3 zones.

Any ideas why.

Pete67

Is is flowing from the expansion tank via the overflow (routed to outside the house) or is there water flowing from the vent back into the expansion tank?

Hedgecutter

Pete67 wrote: »

Is is flowing from the expansion tank via the overflow (routed to outside the house) or is there water flowing from the vent back into the expansion tank?

Via pipe to outside house through soffit

Pete67

Could be either the ballcock is mounted too high in the tank or the overflow is too low, the water level will rise due to expansion when the heating is on.

If the normal water level (with everything cold) is too high or the overflow is too low then some water will be released via the overflow when the system heats up. When it cools down again the level in the tank will drop and any water lost will be replaced via the ballcock, so the cycle will repeat each time you switch on the heating. There should be only a few inches of water in the expansion tank when cold to leave room for expansion.

The other possibility is a pinhole leak on the coil of the hot water cylinder, especially if the water level in the cold water storage tank is higher then the expansion tank, which is often the case.

Wearb

No leak when heating off?

Circulating pump may need turning down and balance valve opened if only using hot water at this time of year.