Grant Combi Max V3 oil boiler - low pressure switch?

Hi,

Having recently replaced a leaky PRV in the above boiler I noticed that the low pressure indicator light failed to illuminate when the system was empty.
I'm looking to replace the pressure sense switch (which I'm assuming has failed stuck closed as it shunts the indicator neon which is in series with the boiler mains supply) I notice the switch assembly seems to plug into a metal bush screwed into one of the boiler HW pipes. The switch is held inn place with what looks like a small metal clip.
However, if I remove the switch using the clip will this cause the system to instantly depressurize or is there some diaphragm in between the switch actuator and the "wet side".

Thanks in advance,

Pete

Pete7457
October 2009