Everything seems normal except after it fires (burners all light), the flames go out but the boiler continues to run. Sometimes the flame goes out after a few seconds, sometimes longer, like a few minutes. I don't smell gas so I don't think it's a dangerous situation but I'm hoping this is an easy fix..
Weil Mclain Troubleshooting
these symptoms unfortunately could have a number of causes which will require an amount of testing. your best bet is to get a heating engineer to do it for you.
It would be helpful to know the model number of your boiler, and whether it is a standing pilot, or intermittent pilot unit, and whether this happens right away (while the boiler (and house) is still cold), or only after it is warm. Single-fire (non-modulating) house heating boilers work as follows: a) The thermostat calls for heat. The boiler fires and heats the water in the system which is then pumped through the radiators. b) There is a high-limit setting on the water temperature to prevent the boiler from over heating the water. This can range anywhere from about 160F (cast-iron standing radiation) to something below 190F for fin-tube radiation. If the water reaches this temperature _before_ the thermostat is satisfied, the boiler will stop firing, but the circulator pump will continue to run as long as the thermostat calls for heat. As the water cools, the boiler will fire again for anywhere from minutes to seconds. c) Once the thermostat is satisfied, the circulator pump and the boiler will shut off. The phenomenon you describe is most common with cast-iron radiation with a large thermal mass, but can happen with any form of radiation. If this is not the case, it is important to know the model number/size/age of your unit as there are many types of pilot systems on these beasts each with its own little quirks.
