MM #42 pump switch failures

steamup

Are other contractors having trouble with the McDonnell-Miller #42 LWCO & Pump Control? Specifically, the pump switch sticks closed. 

One contractor in the Cincinnati area has had numerous failures in the last few years and is looking for feedback or alternatives. He’s not too computer savvy, so I told him I would check with a national audience, since the rep is saying that there isn’t a problem. 

Thanks 

EBEBRATT-Ed

MM always says there is no problem. "your the only one that has had an issue"

I don't know about the #42 but I have had issues with the #150 pump controls after they got rid of the mercury switches. They may use the same switch.

I had one that would flood the boiler at random times and keep the feed pump on. Yet every I tested it took apart the control and made sure the control body was clean the piping to the boiler clean etc it would work for a few days and then flood the boiler. Finally replaced it.

One of my coworkers had the same issue on another job.

steamup

Thanks Ed, sounds like the same issue and started happening about the time they switched from mercury switches to the "snap action" switch.

EBEBRATT-Ed

@steamup
Exactly

Jamie Hall

Sort of a side comment. The old mercury switches were incredibly reliable. Whether they were in a thermostat or pressure switch or float controller of some kind, they just simply worked. And they continue to work. If you have a control with one, keep it... mechanical contact switches -- even the most expensive aviation grade ones -- may be reliable... enough. But "enough" is nowhere near what the mercury ones were.