Hot Water Circulator Pump/Aquastat question

PoorerRichard

We have a 103KBTU IN, induced draft (83% efficiency) gas boiler hooked up to a hot water baseboard heating system on one zone. Our hot water for the house is supplied by an on-demand gas system separate from the heating. The circulator is a 25 year old Grundfoss 1/25 HP on the return loop. We're retired now, and while the system is well maintained, and running well, I want to try and wring out as much efficiency as I can. Investing in a new High Efficiency boiler would not be a smart move, considering our ages, LOL! Anyway... the smart thermostat has an adjustment for how many "calls" per hour, which I dropped from five to three. It's a 2400 square foot, single floor house with decent insulation, but a bit of glass. I was thinking that there might be a setting in the aquastat that kept the circulator pump running longer, to get as much heat from the water in the boiler longer after the burner has shut off. Seems wasteful to just have all that hot water sitting in the boiler. The high shut down is set for 180 degrees. THe add-on circuit aquastat that goes on the return pipe is factory set to go "on" at 105 and shut down at 83 degrees. Do I have that right? Can something be done with the existing aquastat to get a longer circulator run? Right now it seems to shut down soon after the burner shuts off.

STEVEusaPA

There are different aquastats, Hydrolevel & Beckett AquaSmart that may help you with your efficiency. They have features that will hold off the circulator, or use post purge. I think the Beckett will even hold off firing the burner until the water temperature drops.
I don't think the add-on is helping, and may even be allowing your boiler to condense, which is not good. Those settings are too low.
You can try turning down your main aquastat high limit to 160 and see how the system performs, specifically if it doesn't start short cycling.

HVACNUT

What is the make and model of the boiler?

PoorerRichard

It's a Kenmore/Sears 229.964441 Induced draft/intermittent pilot boiler. The standard Aquastat/Control is the Honeywell L8148E or the equivalent. I'm having some issue with it as well.

newagedawn

sounds like you have a cold start aqua stat, use a triple aqua stat especially the ones mention before are great some have 30 diff's which are great energy savers

HVACNUT

That's a rebadged Dunkirk boiler and is designed for a cold start application (to not maintain temperature, but only run on a heat demand).
I would remove the return mount aquastat, then the circ and burner will come on only if there is a heat demand. The burner will probably cycle off and on on limit during a heat demand.
The Hydrostat has post purge, burner hold off on temp rise until the differential is met, and economy settings. It senses return water temp and adjusts the supply temp accordingly. The Hydrostat well must be installed to utilize the low water cutoff option. It can also do outdoor reset in lieu of the economy mode.

PoorerRichard

Thanks, HVACNut! I purchased the Becket 7600B aquastat and will install it today. The past few nights I've been getting up every hour or so serving as a human thermostat as the only control I can use is the emergency shut off. I removed the thermostat and tested it with my VOM. It seems to be fine. The relay must be fried in the old Honeywell Aquastat. There are extra output connections on the Beckett, which gets me thinking about at a later date, adding an outboard relay to separate the induction blower (120VAC) from the Circulator terminals. If the Beckett flue damper contacts could be used to energize the Inducer blower, then I could utilize the Circulator run delay to wring a bit more heat from the hot water in the boiler section. What do you think? Of courwse, this would be a job for the Summer.