Solution 3 - Ensure the pressure switch is functioning properly.
The pressure switch controls the steam pressure in the steam boiler. The pressure switch uses a
spring-loaded diaphragm to open and close a set of contacts, controlling electrical power to the
heating element. Over time, the contacts may become pitted and built up with carbon. If too much
carbon builds-up, it may restrict the electrical current flowing through the contacts, preventing the
element from heating up. The diaphragm can also dry out and lose its resiliency. This can cause
pressure switch to allow the pressure to drop too low before it provides power to the element.
(Newer machines use a Giemme pressure switch, which does not use contacts, but sends a signal
to a contactor. The contactor then opens and closes a set of contacts to power the element.)
1. Remove the machines
top and left side panels.
3. Using a multi-meter, check for voltage
at the top two terminals. If no voltage is
present, inspect the wires going to the
switch from the terminal block.
6. Remove the steam tube
supplying the pressure switch,
and the lock nut securing the
pressure switch to the frame.
7. Leaving the wires at-
tached, pull the pressure
switch from the machine to
facilitate easier replacement
of the switch.
5.Inspect the contacts for pitting
or excessive carbon build-up. It
is possible to clean the contacts
with emery cloth and WD-40.
If cleaning does not restore
power, proceed to step 6.
8. Loosen the screws securing
the wires going to the pressure
switch. Lable each wire and
remove from the switch.
9. Discard the old switch
and install the new switch
in the reverse order.
Return the machine to
service and adjust the
pressure switch to the
desired operating pres-
sure. Generally between
1.2 - 1.5 bar.
2. Remove the screw
and cover from the
pressure switch.
4. If voltage is present at
the top terminals, check
for the proper voltage at
the bottom terminals with
the contacts closed. If now
voltage is present, proceed
to step 5.
