Whenever we fill the boiler up with city water after draining it, we dump the chemicals in thru the manhole.
I think you may have air in system.
yea its called steam locking or air binding
Your right but the problem wasn't the flood was it? It was after the flood when they drained the system and refilled it. Or did they even put any water back in the system. Maybe not a air problem maybe not enough water. Could be a number of things maybe need more info about what all they have checked and done.
The supply lines may have low points where condensate collected many steam systems are not the same as the original design and changes cause low points that are only noticeable when the system floods. You could try to increase the pressure to blow by these points. This is one of many logical possibilities that could cause this type of problem.
One other point and something I am dealing with now at a location. The air vents at some time were capped off and in order to heat the building the pressure was increased from 1.5 lbs to now nearly 5 lbs. We are in the process of uncapping these vents which should allow for a lower pressure in the system etc. Old steam systems are very tricky.
Just a note the system I am referring to has a dry return. It is important to know if you have a dry return or liquid.
Yikes. Oh no my boiler low on water and over heating. Here I'll jus open this BOOM!!!!!
Sounds like a trap issue to me. My guess would be possibly a damaged or stuck riser trap somewhere, but we would need more information about your system layout to diagnose it.