Central Heating & Water Heaters revision notes
Boilers and water heaters — controls, commissioning sequence and spotting an unsafe install.
- 17notes with free previews
- 176questions on Premium
- 9topics
Approved Document L: Controls & Boiler Interlocks
Boiler controls and the interlock principle
The difference between operating and safety controls and what a boiler interlock is for.
Dew point temperatures and boiler condensing efficiency
Understanding return water temperatures for condensing boilers.
Flame supervision: thermocouples and flame rectification
How the device that shuts the gas off when a flame goes out actually senses the flame.
Manual reset overheat cut-out safety controls
Why high limit thermostats are manual reset and how they protect the system.
Motorised valve controls: S-plan and Y-plan auxiliary switches
Understanding switched live wiring and auxiliary microswitches on central heating valves.
S-plan and Y-plan: two common heating control layouts
How the S-plan and Y-plan layouts route heating and hot water, and how they differ.
BS 6798: Boiler Commissioning & Servicing
Calculations: heat output & efficiency
Approved Document L: Boiler Flue & Condensate Design
Calculations: heat output & efficiency
Approved Document L: Boiler Flue & Condensate Design
Calculations: heat output & efficiency
Approved Document L: Boiler Flue & Condensate Design
Fault-Finding and Unsafe Installation Signs
A structured approach to boiler fault finding
A repeatable way of reasoning from symptom to cause instead of swapping parts at random.
No hot water from a combi: a fault-finding checklist
An ordered set of checks for the common complaint of a combination boiler giving heating but no hot water, or none at all.
Why radiators run cold: air, sludge or balancing
A way to reason about cold radiators from where the cold is, pointing to air, sludge or a flow problem.
In-depth guides for this module
Longer walkthroughs that sit alongside the revision notes.
CENWAT revision guide: boilers, water heaters, controls and flues
Revise CENWAT in job stages: can the appliance be installed here, supplied and flued safely, commissioned properly (gas rate, combustion checks) and controlled with full boiler interlock — and what must be proved before handover. Gas rate and heat input are the high-value method questions.
Flue flow and spillage test procedure: open-flued gas revision guide
Flue flow checks the chimney route; spillage checks that products of combustion are not spilling back into the room while the appliance runs.
More gas modules
Every module has its own revision notes and question bank.