Level 2 Plumbing Revision: Topics Examiners Ask About

Level 2 is the biggest jump in the course. You move from making joints to understanding whole systems, and the exams expect you to know why each part is there as well as what it is called. These notes follow the order most colleges teach the units in.

Scientific principles

• Pressure from height: every 10 metres of water above an outlet gives roughly 1 bar. A loft tank 5 metres above a shower gives about half a bar, which is why gravity showers are weak.
• Expansion: water expands as it heats, which is why heating systems need either an open feed and expansion tank or a sealed expansion vessel.
• Capillary action: what draws solder into a joint, and what can pull water up through a badly set overflow.
• Corrosion: electrolytic corrosion happens when dissimilar metals meet in water, such as copper and galvanised steel.

Cold water systems

Learn the difference between direct systems, where every cold tap is fed from the mains, and indirect systems, where only the kitchen tap and sometimes others come from the mains and the rest are fed from a storage cistern. A storage cistern installed today needs a close-fitting lid, insulation, a screened warning or overflow pipe, and a service valve on the inlet.

Backflow is a favourite exam topic. The regulations sort water into five fluid categories, from category 1 (wholesome drinking water) up to category 5 (a serious health hazard, such as the contents of a WC pan). The higher the category at the outlet, the stronger the protection needed between it and the supply, from a single check valve up to a physical air gap.

Hot water systems

Know the vented cylinder (fed from a cistern, with an open vent pipe), the combination boiler (heats mains water on demand) and, in outline, the unvented cylinder, which you will study in depth at Level 3. Stored hot water should be kept at 60°C to control legionella bacteria, and it should reach the taps hot within about a minute.

Sanitation and waste pipes

Traps keep foul air out of the room. Most traps on basins and sinks hold a 75 mm water seal; baths, showers and WCs typically 50 mm. For unvented branch pipes, learn the maximum lengths from Approved Document H, often asked as:

Appliance	Pipe size	Maximum branch length
Washbasin	32 mm	1.7 m
Bath or shower	40 mm	3 m
WC	100 mm	6 m

Exceed them, or drop the pipe too steeply, and the trap can siphon, leaving the room smelling of drains. That is exactly the kind of problem we are called to fix: see our guide to a sewage smell in the bathroom.

Central heating

Compare the open-vented system (feed and expansion tank in the loft, open vent over the cylinder) with the sealed system (expansion vessel, pressure gauge, pressure relief valve and a filling loop that is disconnected after use). Learn the order of components around a system and why the pump position matters. Our article on boiler pressure that is too high shows how these parts behave when one fails.

Above and below ground drainage

Learn the parts of a soil and vent pipe (stack), where branches may join it, and why the top is left open above windows. Below ground, know the purpose of inspection chambers at changes of direction, the idea of a self-cleansing gradient, and the difference between combined and separate foul and surface water systems.

Revision tips that work

1. Draw each system from memory on a blank sheet, then check it against your notes.
2. Make one card per number: trap seals, pipe lengths, temperatures, fluid categories.
3. Explain a topic out loud as if to a customer. If you cannot, you do not know it yet.
4. Do every past or practice paper your college gives you, under timed conditions.