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short cycling and poor heat distribution

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Posted by Pete T on January 28, 2008 at 18:52:02:

Boiler: Peerless 63 series with Vaporstat control
Thermostat: Honeywell T87, single wire, anticipator intended for .4 setting
Piping: 1-1/2" steel, single pipe, with Vari-Valves

Situation: running at 315 therms per month, 1,900 sq ft house, thermostat set to 62

Replaced 60+ yr. old boiler, all near-boiler piping, gas lines from meter to boiler, thermostat & wire, and all radiator valves. Boiler purged and original valves replaced 2 weeks after install.

Initial Problems:
Hammering - so hard that that it blew the tops off of 2 valves, and spitting rusty water out of valves on 2nd floor
Excessive water bounce - disappeared from sight glass
Short cycle - minute and 15 seconds on, off just long enough for flue motor to cycle
No heat in house - house temp running about 4 degrees under thermostat setting

Changes to system so far:
Replaced all Vari-Valves
Adjusted poorly pitched lines
Pressuretrol replaced with Vaporstat
Auto water feed disconnected
Near-boiler piping reworked from double-pipe-out to single-pipe-out
Switched thermostat 2x - t87 to digital back to t87

Replacing the valves, installing Vaporstat, and adjusting the line pitch mostly fixed the hammering and water bounce. Peerless has been out twice, and inspected the whole system from top to bottom - the boiler is appropriately-sized for the run and the fins per inch on the pipe.

The only way so far to get heat to the house is to set the thermostat anticipator to 1.2 - boiler long-cycles, and steam makes it through the system, including the 2nd floor. But the gas usage is excessive, and there is black char (dust) on the floor under the boiler, so the boiler is almost certainly getting damaged from the excessive heat.

Any ideas as to cause and solution?

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