Posted by Harold Kestenholz - Hydronic Network on March 03, 2001 at 15:33:30:
In Reply to: Qs re hot-water-system (sudden increase in) PSI&temp. posted by Michael Poppers on February 27, 2001 at 13:50:23:
With all the excellent clues you have given, it is possible that you have localized heating of water to steam inside the boiler due to your failing circulator. This would cause a rapid temperature and pressure jump, luckily not enough to dump the water from the system. The pressure should not exceed 25 psig on a 30 psig relief valve as this is the resetting pressure once the valve has popped. If the system pressure rises above 25 psig consistently after your circulator is repaired or replaced, get a larger expansion tank or put another one on a manifold with the old one. There are pictures how to do this in the free lessons at http://www.hydronic.net
Severely black water can be corrected by flushing the system with clean water, not chemicals.