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Help me figure out which plumber has correctly identified the problem. We have a 4-story, 2-family house on a single zone old fashioned steam radiator system. The boiler is not brand new but not ancient. House was unused for several years before we renovated, and not well maintained in the years before that. The problem is that the bottom floor runs about 8-10 degrees cooler than the rest of the house (thermostat is upstairs). Bottom floor has low ceilings, insulation, and no discernable drafts. This is not a problem of “heat rises.” The problem is the room where the thermostat is located reaches temperature before the bottom floor has had a chance to heat up.

Plumber A says — we need to clean the sludge out of inside the boiler (my guess is nothing like this has been done for years and years, but I don’t know how necessary it is). According to plumber A, there must be a lot of sediment settled in the boiler which apparently causes the boiler to think the steam pressure has built up throughout the system before sufficient pressure reaches down to the lower floors. He says that, when the boiler is on, steam goes through the pipes to the top floors first and the pressure is supposed to build up from the top down until it reaches the requisite pressure to shut the boiler but in my case the boiler cycles off due to it thinking the pressure is all there before the steam pressure fully builds up on the lower floors. This seems credible because I have observed the boiler cycling on and off every 2-3 minutes while the thermostat is calling for heat, but I question the diagnosis because the radiators do get hot on the ground floor. Plumber A says I am wasting a lot of energy (and money) having the boiler cycle on and off and that cleaning the sediment out of the boiler will alleviate the problem.

Plumber B says none of what plumber A says matters. We should get new valves on the upstairs radiators to limit how much heat they put out so that the upstairs reaches the thermostat temp more slowly, giving the radiators downstairs time to heat up before the thermostat turns the system off. His solution seems like it may work but I dont’ know if he is right that plumber A’s diagnosis is irrelevant to the problem. Also, the solution seems wasteful; I don’t want to run the heat longer, especially if Plumber A is right that I am wasting energy with the boiler cycling on and off. But if the cycling is, in fact, normal, or unrelated to my uneven heat distribution problem, I want to make sure I fix the problem.

Anyone experienced enough with these old steam systems to have a sense of who’s got the better diagnosis here?