oil boiler cycling -- too frequent?

Tman · 2009-02-11T02:16:12+00:00

Would like a perspective on cycling of an oil boiler.So I replaced a spent Burnham RSA110 steel boiler with a Peerless WBV cast iron boiler. Everything else remained the same -- still three zones, configured essentially the same way, and the same size / model Taco circulator.I was expecting, due to the increased water capacity and thermal mass of the Peerless (new) boiler, plus a smaller nozzle, that there would be less frequent cycling. However, the new boiler, when all three zones are cranked open, cycles approximately like this:- 2 minutes on- 4 minutes off.That strikes me as excessive, and as more frequent than the previous RSA boiler which is counter-intuitive to me for the reasons above.Does this rate of cycling seem excessive and/or inefficient for a new cast-iron boiler ?A couple more data points:The Aquastat is different, a newer digital model, but the settings are confirmed the same: 180F high limit, with a (fixed) 10F differential. I made sure the new digital temp sensor bulb was well seated in the well. Judging both by the digital readout on the 'stat and the temp guage, the new Aquastat seems to be doing the job "OK".The old boiler had a nozzle that flowed 1.00 GPH. I put in the smaller of the nozzles available on the new boiler -- it flows 0.85 GPH. Now I know that the cast-iron model will be a tad more efficient, but I would not expect shorter on-cycle times with the lower flow rate!I had the burner adjusted by the oil company guy -- seems to have the right flame -- but he has no idea about the cycle times.I'm pretty sure the system is substantially evacuated of air, and the zones seem to be flowing well. And in the correct direction of flow :).The old boiler was about 150 lbs of steel and 8 gallons of water. The new one is about 400 lbs of iron and 17 gallons of water.Everything tells me the cycle should be longer -- but it's not. What else could I be missing.Tman.

Feb 11, 2009 20 Replies

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dsgreenawa 17 years ago

------------------------------------- Is is possible that the circulator turns off when the burner turns on? This would only require the burner to heat the 17 gallons of water in the boiler - which would take about 2 minutes to heat up by 10 degrees. Takes about

4000 BTU. If the circulator would continue to circulate while the burner runs it would have additional load and would not cycle so shortly.

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