Got a boiler model number & make? According to
a remanufacturer's exceedingly brief description it should be adjustable from 5F to 45F differential:
" 5 - 45°F diff. reverse L6010A"
If the thing still works, you could install a lower-cost heat purging economizer control and get a MUCH increased hi/low differential, and it will pay for itself in 2 heating seasons or less if gas, less than one heating season if oil or propane. Something like the Intellicon HW+ (formerly called the 3250 HW+, also sold by Beckett as th e"Heat Manager") works fine. Full online retail they run about $200, but older versions can be had for under $100 (new or used) at times on secondary markets such as eBay or craigslist. You have to be able to figure out the boiler schematic, and have some electrician sklls, but it's definitely not rocket science as a DIY project to
install and program one.
These things use the secondary sensor strapped to the outlet piping of the boiler as close to the boiler as possible, and use that sensor to set the low-limit. The existing aquastat sets the high limit. When there is a call for heat the pump runs but the boiler doesn't fire until the economizer's low-limit temp is sensed at the output pipe. (The Intellicon has a second sensor to use for indirect water heater zones, but IIRC the Beckett versions don't.) They also "learns" your system based on recent burn cycle history and ancipates the end of a call for heat based on the duration of the calls for heat and the temperature sensed, and cuts the burner ahead of the end of a call for heat, parking the boiler at a lower standby temperature for lower standby losses. The net effect is lower average boiler and system temperature while still being able to deliver the full-0n high temperature as needed, with much fewer (but longer) burn cycles, and lower burner operation time overall. For a typical 3x oversized gas boiler with high-temp radiation the net annual saving tend to be in the 15% range +/-3%, but 20% isn't unheard of. It really depends a lot on your system radiation, zoning etc.
There are similar retrofit boiler economizer controls with more bells & whistles than that, but anything more than the simplest isn't going to be worth it if you're getting rid of the beast in short years.
With a gas boiler programming the economizer as low as 130F is fine, but for oil 140F is the limit or you'll end up with excessive (very acidic) flue condensation or even condensation on the boiler plates, but you then set the high limit of the aquastat to the max (typically 210-220F) That allows you a 70-90 F differential, making maximal use of the thermal mass of the boiler and system.
If using the L60101A as-is and the burn times are <5 minutes it's worth increasing the differential to improve burn times, even if it means having to raise the hi-limit to keep it from dropping in to the condensing-risk zone. Without heat-purge that increases the standby losses, but it avoids the start-up losses and delivers fewer but longer burn cycles, and greater net efficeincy (though nowhere near as effective as a heat purging economizer control.)
