*PLUMBERSSTOCK EXPERT* responded:
Thanks for asking help from the PlumbersStock team. Although there can be a number of reasons as to why your boiler is overflowing, one of the most common causes is due to a clogged water feeder valve. Have you been flushing your McDonnell & Miller 101A water feeder out every week? Weekly flushing or "blowing down" of the feed water control is recommended during the heating season to drain the lime and sediments (that cause clogs) regularly. When you said "sticking", do you mean that it's not shutting off? If so, you can try the troubleshooting steps (no.4) on page 7 of this Instruction Manual. You can also contact McDonnell & Miller at 847 966-3700 for more instructions. If you suspect that you have a faulty water feeder, you are always welcome to purchase a new one here at PlumbersStock.com. Thank you for letting us help you.