Gas Boiler Electrical Wiring

Wiring diagrams for oil burning and water boilers are noted.
Gas boiler electrical wiring. The things that needed to be wired were thermostat aqua stat low water cut off and a gas vent damper. The load is now a boiler. See figure 4 page 20 this wiring diagram shows 120 v coming from l1 of a circuit breaker through a switch powering a boiler control and returning through l2 back to the neutral bar of the circuit breaker box. I want to replace a gas fire.
Gas boiler wiring application guide u s. Featuring burnham brand iq boiler control and intelligent hydronic control systems. British gas engineers detected a shocking 26 000 unsafe or dangerous gas and electric appliances during home visits in the first eight months of this year. Lets say its a 120 v gas fired boiler that controls a few base board radiators.
If some 1 can take some time to explain how to wire these things id reallly appriciate it. Will a gas engineer be able to buy the model i like or do i have to go to a gas fire shop. Intelligent hydronic control 2013 u s. Es2 esc series 3 series 2 boiler control.
Last summer we had a complete refurb of a house we d just bought. The most common faults were found in boil. Most of the wiring diagrams are for natural gas powered steam boilers. Is it a legal requirement to have a room themostat fitted with a new boiler heating system.
This included replacing the old boiler and we now have a combi. However most gas boilers you will be working on have 24 v controls.