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Short Cycling - How to Diagnose and Fix?
I'm new to home ownership and definitely steam, but learning quickly. Just finished "The Lost Art of Steam Heating Revisited" after "We Got Steam Heat!". I think I enjoyed them too much!!
This first winter my heat system started with water hammering and one baseboard convector not working. Heat is working great now and fairly quiet but my boiler is short-cycling after the system heats up and and I'm unsure how to proceed. With the current setup, once the convectors are warm, the boiler will turn-on for 2 minutes and then off for 1 minute, until the Thermostat is satisfied.
What I've done so far:
- I replaced all existing air vents (Vent-Rite #1 and main - Vent-Rite #75) with Hoffman #40 and main vent with Hoffman #45. They no longer leak and drip and all convectors are heating up fully.
- My plumber put a tee and nozzle on the safety release port so that I can skim the system. This made the water hammering go away. I have probably repeated this about ten times but not seeing any additional changes and the water is pretty clear, although I see rust particles in the glass when the boiler is running. Should I continue to skim?
- I have installed a Nest Thermostat, initially with 2-wires. I now have a common wire added as well and last night enabled the "True Radiant" setting as well. This replaced an old Honeywell mercury/bimetal Thermostat.
- I have replaced the 30 PSI gauge, but this one seems worse than before. I just added a brass pigtail to this section and put a tee for the 30 PSI gauge, but also added a 5 PSI gauge, which seems far more accurate.
- I have used the 5 PSI gauge to calibrate the Pressuretrol to cut-off ~2.0 PSI and cut-in ~0.5 PSI.
What I know:
- It's 1-pipe steam that was originally oil (built in 1950).
- There are 11 in-wall convectors of various sizes on the first (and only) floor.
- The boiler is a natural gas Burnham installed in 1991 (~28 years old). It is rated 108,000 BTU gross.
- The "A" dimension is approximately 28 inches (between the water line and bottom of return pipe).
- All the convectors are sloped correctly and the air vents are elevated above the convectors.
What should I do next? Advice and suggestions are greatly appreciated.