low back, spillage, or a bad thermocouple.
If the tub is not getting hot water the issue is probably with the hot water heater. The hot water heater may have tripped a breaker or the pilot light went out.
it could be from the hot water heater if it's not turned off. hot water expands pushing out more water when cool the heater can suck in air to fill the voide.
Disabling the ignition or disconnecting the gas source is a good start.
Check if the water supply line valve underneath the sink is on or off .."On" will be turning counterclockwise ,If not look for the hot water heater and make sure the water supply valve is turned on.
Central heating systems usually heat on a different system from the hot water heater, unless the main heater is a combination furnace/hot water heater. If this is the case, it could be because the outflow of hot water is greater than the ability of the furnace to heat the water.
Have you turned the control from Pilot to On? Have you increased the temperature setting?
If the pilot light is on, the heater should come on by itself. If the pilot light is off then it has to be lit. If it will not stay on, the thermocouple is bad.
Gas not turned on to water heater. Gas valve on water heater not set to pilot setting. Faulty gas valve. Igniter for lighting pilot not working.
Yes
Gas water heater has an orifice for main burner and for pilot light, if not electronic ignition.
The water continues to run into and out of the water heater. There is just no flame to heat it up.
THERMOCOUPLE or defective gas valve
small amount
Same as any hot water heater. Turn the gas valve to off.
You don't. If the heater has an electronic spark, then it doesn't have a standing pilot to light. The spark lights the pilot when there is a call for heat, which in turn lights the burners. If the heater is on and the pump is RUNNING, the heater should light automatically when the water temperature is lower than the heat setting.
is the lines on the thermal coupler and pilot light for a hot water heater supposed to get hot
No, it is not dangerous. (Unless you are working with a water heater that is 20+ years old.) In any modern hot water heater, if the pilot light goes out a fail-safe will go off - preventing gas from leaking out. Also, there is a sensor so if there is not enough air-flow or oxygen with the water heater, it will shut off the gas.