Gas boiler: booster pump/thermostat trouble

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Old 11-29-05, 07:29 PM
Cynthia
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Gas boiler: booster pump/thermostat trouble

Sorry this is long, but here's all the background:
We have a gas-fired hot water radiator system (Weil McLain model CGM-4 boiler with Bell & Gossett Little Red Booster Pump, both 15 years old). Toward the end of last heating season, it seemed the anticipator in our old thermostat (20+ year old Sears “Automatic Set Back/Set Up Thrif-T” mechanical/mercury programmable thermostat) was no longer working right. Specifically, the heating system suddenly started running for only a few seconds at a time. When I adjusted the anticipator mechanism, it was much better but I never really got it to where it was before.

So early this fall, we decided to replace the old thermostat with what Sears’ website indicated was the current equivalent model: WhiteRodgers #1F80-261 (digital programmable). Now, the problem is that, while the boiler cycles on and off appropriately to keep the water temp at 170F, the booster pump runs continuously (which it did not used to do). For example, the pump runs non-stop for two and a half hours while our house warms up by 5 degrees. The new thermostat has only 2 anticipator settings (fast and slow) but it seems to run the same with either setting.

With our radiator system, it’s not unusual to take a couple hours to gain 5 degrees (from an overnight low of 63F to daytime set-point of 68F) but in the past, the pump always cycled on and off during that time. And I think it still should; once the radiators are hot, they stay hot for quite awhile before they need “refreshing.”

So what’s wrong here? Did we get the wrong thermostat for our system? Might there actually be a problem with the pump that predates the new thermostat? Or what?
 
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Old 11-30-05, 07:45 PM
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Circulator cycling

The circulator should run the entire time the thermostat is calling for heat. The burner may cycle on & off but the circulator should keep running.
 
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