low water cut-off / pump controller

William Faust

I have a McDonnell Miller (MM) 150SHD low water cut-off and pump controller. The MM literature that came with the unit says that I should replace the head mechanism every five years. These heads are on the order of $400. A lower cost alternative is to replace the existing head's switch assembly. MM's caveat to the latter is that it may need "field testing." What is there to installing the switch assembly?

DanHolohan

I think this has to do

with the way they set the switches at the factory. I've watched this being done. They apply pressure to the unit while setting the switch, and then they seal the switch. The pressure affects the stroke distance of the control. Tough to do in the field under steam pressure. They use air pressure at the factory.

Just a guess.

$400 every five years is still cheaper than a new boiler. And cheaper than five year's worth of oil changes for your car.

William Faust

head v. switch replacement

Yup, I'd better replace the head.