is your boiler also kettling (bubbling when hot) if so the main heat exchanger may be partially blocked and your whole system in need of chemical flushing.
Or if the problem is on dhw only, it maybe a blocked - partially blocked dhw heat exchanger allowing the water to boil due to reduced flow, this would send your boiler to lockout on the dhw high limit stat.....
either way should be a straight forward enough check for a technician to perform, all they have to do, is when it's locking
out to check the limit stat with their multimeter to see if thats where the problem lies!
T
May 2008
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