Temperature Fluctuations
Fluctuations in temperature in the boiler during a heating cycle should be steady, and should remain within certain setpoints. These setpoints vary depending on the type of system you have. Although certain condensing boilers can run at lower than usual temperatures, boilers that run too low risk premature failure.
Running too hot can be problematic too, even dangerous. While a boiler that runs too hot leads to overheating and/or overstressing of connected components resulting in premature failure, a boiler that goes into “runaway” can become quite dangerous.
Pressure Fluctuations
Fluctuations in boiler pressure boiler during a heating cycle should also be steady, and should also remain within certain setpoints. Boiler system components are designed to operate within certain parameters, and exceeding the high or low range indicates failure of one or more of these components.
Low pressure is typically caused by a malfunctioning fill valve or a leak in the system or system piping. High pressure is caused by many things, such as a malfunctioning fill valve, malfunctioning expansion tank, domestic water pressure from a leaking tankless coil or leaking indirect water heater coil, malfunctioning limit controls and malfunctioning control boards. High or low pressures can also present due to improper placement of circulator pumps in the system piping, which can alter pressure readings at the gauge(s) at certain points in the heating cycle.