I have a 25 year old utica gas boiler that works normally when the boiler is cool. The thermostat calls for heat the boiler fires up and the hot water circulates. the problem happens when as the hot boiler cools off and reaches the low end temp when it signals the burners to relight; it relights for a moment and then immediately turns off. It will continue to cycle off and on until the thermostat is turned off. then we wait for the boiler to cool down (an hour or two) at which time the boiler will repeat the above cycle.
Check the heat Antisapator on the thermostat, or replace the thermostat.
SOURCE: Pilot goes out after heating cycle
Check regulator on the unit.
Check pilot unit on the heater
use soapy water to check for leaks if see bubbles turn off main gas supply valve.
always turn off gas supply before any checks or repairs are made
when all else failes call your local gas provider to check heater and gas supply
SOURCE: I have a GE (Rheem) SmartWater SmartShield Sensor gas cut off
The click you hear is the gas valve shutting off flow. It does that because the thermocouple (a rod sticking into the flame of the pilot) voltage drops, usually below 13 millivolts or so. Might be a loose connection from thermo to valve body (should be finger tight plus 1/4 turn) or a bad thermo ($13 at Lowe's). Good Luck.
SOURCE: Furnace cuts off before reaching set temp.
You can make sure it is not the thermostat by crossing or jumping the R and W terminals (or associated wires) together. This will keep the furnace calling for heat. As it is approaching set temperature, get in front of the furnace and inspect the air filter to make sure it is clean, watch the control module for any error codes that may be turning off the system prematurely.
On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the igniter. The igniter will glow and you will be able to see it if viewed thru the small inspection port. Once the igniter gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.
What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the igniter does not energize (bad control, bad igniter), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not light (dirty pilot), the burner does not light (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).
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