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Posted by HeatPro on February 19, 2006 at 11:10:04:
In Reply to: lack of heat posted by capemike on February 19, 2006 at 09:35:51:
Completely changing controls and thermostats is a clue that the repairman hasn't a clue as to the cause or cure.
Use a thermometer to read the temperatures at the beginning and end of each circuit. There should be at least or less than 20F degrees difference between beginning and end. If the temperature difference(drop) is greater than 20F, there is insufficient pumping. The usual cause is insufficient purging of air so there is a partial air blockage.
http://64.226.150.132/hydronic/service/purgeair.htm
Identifying which type of circuits, fuel, burner, zone valves, thermostats by model and number can help find further reasons. Taco zone valves draw a lot of current and have to have the thermostat anticipators set to .9 amps or the thermostats go on and off fast so the house never gets to temperature.