BOILER SYSTEM DIAGNOSTICS - Pressure Switch
PROBLEM
POSSIBLE CAUSE
SOLUTION
Switch activates when
pressure is reached but
boiler not firing
Control not flowing through switch
A multimeter can indicate if the proper voltage flows through the boiler side of the switch. If not
the switch may not need replaced.
Switch improperly wired
Switch may be improperly wired for its function.
Switch bad
If wiring is proper and still no current flow when activated, switch may need replacement.
Switch does not activate
Plunger fouled or stuck
Check pressure plunger to see if it will travel freely. If not, the passage may need cleared.
Plunger not moving far enough
Check to see if the plunger is traveling far enough to depress the microswitch. Adjust if
necessary.
Switch activated manually
Current not flowing through switch
If switch activates manually but boiler does not fire, current may not be flowing through. The
switch may need replacing.
Microswitch not properly adjusted
Microswitch may need readjustment so plunger can trip in.
Switch bad
Replace switch with another one.
Problem elsewhere in the system.
If switch works manually and current is flowing properly, the problem is elsewhere. Try other
boiler diagnostics.
BOILER SYSTEM DIAGNOSTICS - Vacuum Switch - Optional
PROBLEM
POSSIBLE CAUSE
SOLUTION
Switch activated manually
Improper diaphragm movement
Replace switch if improper diaphragm movement is detected.
Low water flow
Correct problems related to inadequate water flow.
Air leak in or punctured diaphragm Replace vacuum switch if diaphragm shows an air leak or hole.
Switch shows continuity
when activated
Problem elsewhere in system
If vacuum switch works properly, continue with other boiler control diagnostics.
Switch does not shows
continuity when activated
Switch contact bad
Replace switch with another one.
