I have a 50 year old open vented CH system with a combined cold feed and vent. I have a service (isolating) valve on the F&E tank mains supply to its ballcock which I keep permanently closed, I open this ~ every two months or so to check for any leaks etc and I have NEVER seen a drop of make up water required, the isolation valve is tight, there is absolutely no leak past if I check by draining off a few liters to lower the ball. A pin holed cylinder coil would not allow water from the CWST to "keep" the F&E tank full as the F&E is mounted above the CWST.
It seems inconceivable that no make up is required with a OV system, there is certainly no corrosion causing any gases to keep the level up, some of the rads are > 40 years old and I throw in the odd drop of inhibitor only if I drain down (one) rad every few years to renew a TRV or whatever.
It seems inconceivable that no make up is required with a OV system, there is certainly no corrosion causing any gases to keep the level up, some of the rads are > 40 years old and I throw in the odd drop of inhibitor only if I drain down (one) rad every few years to renew a TRV or whatever.
