I've had a reply from Honeywell on the cause of the problem, and re the Megaflow sensor, see below...
The issue was not related with the zones, was just a matter of re-registering the MAC id.
Regarding the Megaflow tank, you should leave the existing control in place and slide the sensor down to the same pocket.
Regarding the Megaflow tank, you should leave the existing control in place and slide the sensor down to the same pocket.
Comment