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Your boiler was likely installed in a space that does not provide sufficient combustion air.
The better and long-term solution is to provide a proper vent to provide the needed air. You seemed to have figured this out on your own.
The next logical question is where to put the vent and what size is needed.
I have always felt the answer to this question is not found in the law or 'code,' but what is safe.
The major concern to me is carbon monoxide production by the boiler. CO is made when there is not enough air to completely burn the gas the gas that is firing the flames.
The code seems a good place to find a 'safe' number for the amount of air needed.
The answer to what does the code say, is not easy to determine. There are a number of boilers in the US Boiler, Burnham Series 2 (Model B) product line. The difference is BTU input rating.
The install manual does not provide venting information, instead it points NFPA 54. NFPA states that JHA makes the final determination.
The NFPA answer requires knowledge of the furnace, and the amount of air in the house that can be used for combustion.
The amount of air, found through a formula based on measured or calculation of air provided by the house.
The issue of proper venting should also be addressed, this requires more, and different ventilation.
I know this did not give you a satisfying answer to your question. The CO issue is enough that you should have the needed changes made.
Questions Is the floor a radiant system with the piping in the floor like concrete or under the floor (tubing running under the floor between the joists). It makes a difference. You said the system was steam but if is that would be odd. I am going to say that you mean hot water. One note; a radiant floor heating system has a large lag time, the house does not respond quickly to a thermostat change of a quick weather change. Also if it is a radiant slab system in concrete the slab water temp is rarely above 140 degrees F. I think you need to call a heating expert.( D. George)
Best Answer
Dangerous? If it malfunctions and an over-pressure event occurs, that's dangerous. Whether or not a functioning gauge will provide early warning or not would depend on the experience/knowledge level of the gauge reader and the nature of the malfunction.
Are you required to have a functioning pressure gauge? Most likely you are but it may depend on the duty rating (BTU), type of occupancy, and where you live. Some boilers in some states require regular documented inspections which include a pressure check. Inquire with your local code enforcement agency, although you may not like what you find out about responsibilities attached to steam boiler operators.
But the rules are written in somebody's blood, just do an internet search for boiler explosions and you will see.