For the past 6 months when I shower the water from the boiler keeps
going hot & cold(shower thermostatic controller). By searching the
group & few past posts Have mentioned the air pressure control switch.

Is this easy to replace ie turn elecy off, remove boiler casing & just
change over switch. Since the local suppliers cite them has not being
too expensive & the boiler manual shows easy access to the switch.
Or should I show caution being a gas Appliance. I'm generally quiet
mechanical.

Or secondly could my problem be something else ie barking up the wrong
tree.