This trade does not work on a site
That is the thing that shapes the whole chapter. The work happens in occupied buildings, frequently alone, in somebody else’s house, on systems that store energy. Nobody in the building has had an induction, and the family will use the space while the work is in progress.
So the hazards are not the site ones. They are scalding, stored pressure, carbon monoxide, legionella, and disturbing asbestos or lead in a building nobody has surveyed because it is a home.
The two temperature questions that pull against each other
Legionella multiplies in water between roughly twenty and forty five degrees, so the design principle is to keep hot water hot and cold water cold: stored at sixty, delivered at fifty or above. The obvious way to prevent a vulnerable occupant scalding is to turn that down, and it is the wrong answer.
Thermostatic mixing at the point of use is what lets both requirements be met. It is the clearest example in the whole chapter of a control that looks sensible and creates a worse hazard than the one it solves, which is why it is worth being certain about before the test rather than during it.
Carbon monoxide, and why the symptoms are the trap
Headache, nausea, dizziness and tiredness are the early signs, and they are indistinguishable from flu, which is why people go to bed rather than outside. The pattern that gives it away is everybody in the property feeling ill and improving when they leave.
An appliance can burn perfectly and still kill somebody if the flue does not take the products out of the building, which is why the flue is checked as part of any work on a combustion appliance rather than only when one is replaced. Blocked air bricks and sealed vents from energy improvement work are a recurring cause.
Hot work in an occupied house
Heat conducts along pipes and through joists into material nobody can see from where the torch is, and the fire develops hours after the engineer has left. The fire watch after the work is the control that catches it, and it is the one most often skipped when the job finishes late.
In an occupied property the consequence is not a damaged building. It is people asleep in it that night.
It is the operatives test plus a chapter
Roughly seven questions in ten are core material from the operatives test, so shaky core areas are what will fail you rather than the plumbing ones. The score separates plumbing and heating out as its own line so you can tell the difference.
The plumbing half repeats sooner than the whole bank
Two papers of K questions from a bank of N share about K squared over N. The subject pool is smaller than the core pool, so it repeats sooner than the combined figure suggests. Both numbers are shown above the test, and the revision mode targets what you keep getting wrong.
Common questions
Why is the legionella and scalding pair the question people get wrong?
Because the obvious answer is the wrong one. Turning the cylinder thermostat down solves the scalding risk and creates the legionella risk, since the bacterium multiplies between about twenty and forty five degrees. The correct answer is to store hot at sixty and mix at the outlet with a thermostatic valve, so both requirements are met at once.
Can a qualified plumber work on gas?
Only if they are Gas Safe registered for that category of work. Registration is specific: somebody registered for domestic boilers is not registered for commercial catering. Supervision does not transfer registration, and isolating the supply first does not put the work outside the scheme.
What is a dead leg?
A length of pipe with no through flow, where water sits still and warms towards room temperature. That is the ideal condition for legionella. Dead legs get created every time a fitting is removed and the branch is left in place, so they accumulate quietly over the life of a building.
Why is an unvented cylinder treated differently from a vented one?
Because it is a pressure system holding water above a hundred degrees. If the safety devices are defeated or fail, the contents flash to steam on rupture. That is why the work is restricted to people holding the specific qualification and why the relief valves and expansion vessel are not optional.
What is the pass mark on the plumbing and heating paper?
Forty five of fifty, in forty five minutes, with five wrong answers as the whole allowance. Thirty five come from the core operatives chapters and fifteen from plumbing and heating. The trade fifteen are where the marks usually go, and the legionella and scalding pair is the classic: turning the cylinder down solves one problem and creates the other, and only one of those answers is right.
Are these the questions CITB actually uses?
No, and they are not meant to be. The live bank is sold by CITB and never published, so the free sites offering real questions are copying somebody. These are written from free HSE guidance on legionella, gas safety, pressure systems and carbon monoxide, and each answer links to the page it came from, which is the part no commercial mock test does.
Is my progress saved separately from the other mocks?
Yes. Progress for this paper is stored under its own key in your browser, separate from every other test here, with no account and nothing uploaded. On the specialist half the pool is twenty eight and a paper takes fifteen, so a second sitting repeats roughly eight of them. That number is printed on its own so you can tell practice from recognition.