Why put vent pipes over tanks?

[Dan Robinson]

Think about it a bit more.



Where are you proposing to terminate the vent?


How many deaths have there been directly attributable to a vent pipe discharging over a cws cistern.

 

[Onetap]

Other systems, in fault conditions, do safely discharge to the exterior.

The major advantage of the vented system is that it is simple and almost foolproof.

Discharging the OV outside makes it vulnerable to contamination and freezing. Freezing the OV could cause an explosive rupture of the cylinder.
The failure mode (thermostat welded itself closed ) has been made much less less likely by the revised spec of the thermostats.

The OV on a vented system, if properly installed, should discharge steam, which will blow into the loft and condense in the tank. The T&PRV on a vented system will discharge hoit water, which is why it must be routed to a safe external discharge point or a dedicated drain.

If you want the OV to discharge externally, get a cylinder custom made with a boss for a T&PRV and discharge that externally. It's way OTT, IMHO, and I'm a tad H&S obsessive.