Willy die wrote on 10/11/2019 :
Working on gas boilers and gas appliances is not DIY... Taking off the case
to
an appliance means you have to undertake statutory checks to ensure the
appliance works correctly and safely.

What like the British Gas engineer who installed a water heater for my
parents, where he left the supply pipe spewing out gas into there home
due to his total incompetence?