Boiler Safety Upgrade: Installing a Second Pressure Control in Series

Great advice and no nonsense explanation as usual. Clear, cogent, concise! Mad Dog

Very helpful, I was thinking about adding a second pressurecontrol to my residential, one pipe system. They system runs fine and I have the pressure controller set to cut out at 1.5 psi and in at 0.5. Two questions.. Ray talks about commercial boilers. Would it be worth it to do this on a residential boiler? (I'm thinking yes…). Second question.. Would I better of purchasing a vapor controller?

For background.. the boiler is a bit oversized, so on cold days it does cycle back and forth between at a rate of once every four minutes or so.

Redundancy in safety limit controls are always a good idea.

This goes for hi temp limit controls on traditional hot water boilers as well. Your post is timely. Recently had a 1.5 MBTU boiler hold the burner on. That was entertaining. Big old National CI boiler that could also be outfitted for steam. This hot water boiler released its alter ego steam desires into the boiler room in what must have been a dramatic display of flash steam. We learned exactly how much black muck collects over 72 years in a mixed metals system. The boiler room and everything in it turned black, and the floor thick. Multiple flange seals leaking.
On the bright side, the boiler seemed to enjoy the purge. After thorough cleaning, replacing the aquastat and adding another, stack temp is lower and water temperature rises noticeably more quickly to meet heating load. They lucked out but what a mess.

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This is what I thought. Operating at potentially a lower pressure would only serve to make the cycles shorter. It's so strange because my EDR is 321.3 square feet. This includes a loop that acts more like a hydronic system too (cast iron baseboard). When I calculate the BTUs (240 for steam, 150 for hot water), I get around 72,000. I have all the piping insulated so using a pick up factor of 1.33, works out to 95,000 BTUs, the boiler nameplate is 375 square feet or 90,000 BTUs, so it really shouldn't be oversized. I know my EDR calculations are correct, not sure what I am missing and why the boiler acts like it is oversized.

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BillyS,

Look at your low pressure gauge when the boiler shuts off. Time how long it takes to go down to 2 oz. If it is very rapid, beyond what you would expect from the collapsing steam field, you probably have a radiator vent valve (or main vent valve) that is leaking (possibly due to wet steam). If so, consider replacing the vent valve, possibly a smaller vent valve, trying to dry your steam by lowering the water level in the boiler slightly, lifting the vent valve on a short nipple as extension, etc.

HTH