Gas boiler - continuously cycling

Friend has a gas boiler with radiant heat and noticed today that it starts firing, shuts off, repeats, for about a minute or two before it quits.
The water heater has a flame and has maintained temperature (in the same room) and the temperature in the house has not dropped below the prescribed level from the programmable thermostat (there is water flow through the pipes that provide radiant heat, but there is a whiff of gas that can be smelled during the firing on/off.
I've read where this can be caused by low water flow through the system, or just a dirty burner.
Several service calls have been placed to local service businesses, but have not been responded to yet.
Is there anything to be reset or that can be manually cleaned?
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wrote:

Just to be clear ... the boiler fires, quits, fires, etc. for a minute or two before it quits, but then does so again on the next (pardon my nomenclature) "call for heat" (?) from the thermostat ... there is a correlation between the "click" of the stat and the boiler firing.
However, the temp is near the therm temp, so I don't know if this is "normal" or not, since the water would only need to be minimally heated to remain at temp, but this is the first time that the smell is present.
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