SOLAS Plumbing common mistakes
SOLAS Plumbing · Understand the traps and how to avoid them.
When asked about the minimum depth of cover or the requirement to protect buried pipework, candidates quote a single number they half-remember (often 600 mm or 750 mm) without distinguishing between external buried supply pipes, internal floors, and pipework under a building, and without mentioning the need for a tracer tape or marker.
Depth-of-cover figures appear in several places (water regulations guidance, manufacturer instructions, and site practice) and differ by situation, so candidates memorise one figure and apply it everywhere instead of recalling the principle: protect against frost, mechanical damage and contamination, and record the route.
What to do instead
Learn the principle first (frost protection depth, protection from damage, tracer/marker tape, no joints under buildings where avoidable), then attach the figures to their specific context. When a question asks for a number, state the context you are assuming before giving it.
Candidates describe backflow protection by naming a device ('fit a double check valve') without identifying the fluid category of the risk, the correct protection level for that category, and where in the system it must be located relative to the risk.
Backflow questions are usually written as scenarios, and candidates pattern-match on the appliance (hose, boiler, commercial kitchen) rather than working through the category-to-protection mapping. The categories and device types are easy to confuse under time pressure.
What to do instead
Practise a fixed routine for every backflow question: identify the fluid (category 1–5), state the protection required for that category, then state the location (as close as practicable to the point of use, with no unprotected branch downstream). Drill the category definitions until they are automatic.
On Legionella questions, candidates list control measures generically ('keep water hot', 'flush the system') but fail to give the specific temperature and time controls, fail to distinguish control of hot versus cold systems, and fail to identify the responsible person and the need for a written risk assessment and scheme.
Legionella content spans several topics (temperatures, storage, sentinel outlets, monitoring, roles) and candidates revise the narrative rather than the numbers, so the specific figures and the management framework get blurred together.
What to do instead
Build a one-page table of the key figures (cold storage and distribution temperatures, hot storage and return temperatures, outlet temperatures, sentinel outlet testing frequency, and the timescale for action on a failed sentinel) and rehearse the management chain: responsible person, risk assessment, written scheme, records.
Candidates size or specify pipework and components from a rule of thumb (for example '15 mm does the job') without calculating flow rate, pressure loss, or checking the available pressure at the outlet, and without accounting for equivalent length of fittings.
Plumbing science questions feel abstract, so candidates skip the calculation and rely on remembered sizes from site work, forgetting that exam scenarios deliberately give marginal pressure or long runs where the rule of thumb fails.
What to do instead
Work every sizing question in the same order: required flow rate at the outlet, minimum residual pressure needed, available pressure at the source, then pressure loss over the measured plus equivalent length. Show the arithmetic; even a partly correct method earns marks and prevents silent errors.
When asked about testing or commissioning, candidates describe 'fill it up and check for leaks' rather than the specified test procedure: the test medium, the test pressure relative to working pressure, the stabilisation period, the duration, and the acceptance criteria, plus who witnesses and what is recorded.
Site experience often involves informal leak checks, and the formal test regimes (pressure testing of supply pipework, drainage air tests and water tests, flushing and chlorination of storage) are learned as separate facts that candidates do not connect into a procedure.
What to do instead
For each system type, memorise a five-part test script: medium, pressure or condition, stabilisation, duration, acceptance. Then add the documentation step (test certificate, witnessing, records handed over). Rehearse the drainage tests separately because their conditions differ from pressure pipework.
Candidates confuse the roles of the various fittings and valves in a hot water or heating system - for example mixing up a pressure-reducing valve, a pressure relief valve, an expansion vessel, a non-return valve and a thermostatic mixing valve - and so describe the wrong component in a fault or installation question.
The components look similar in description and are often listed together, so candidates learn the names as a set without attaching each to its function, its location, and the failure symptom it produces.
What to do instead
Make a component card for each: what it does, where it sits in the system, what happens if it fails or is fitted wrongly, and what the symptom looks like to the occupant. Fault-diagnosis questions then become recognition of a symptom rather than recall of a name.
On drainage and above-ground discharge questions, candidates give a gradient or a pipe size without stating the direction of fall, the reason for the gradient (self-cleansing velocity versus prevention of solids deposition), or the requirement for ventilation and trap seal protection.
Gradients are memorised as isolated numbers, and the connection between fall, velocity, and trap seal retention is not reinforced, so candidates answer the number but miss the reasoning marks.
What to do instead
For every drainage answer, state three things: size, gradient, and direction of fall, then add the ventilation and trap seal point where relevant. Explain why the gradient exists (self-cleansing without excessive velocity) so the number is anchored to a reason you can reconstruct in the exam.
Candidates treat water treatment and water quality as a list of chemicals and doses, without linking the treatment to the problem it solves (hardness, corrosion, scale, microbiological control) or to the point in the system where it is applied.
Treatment is often revised as a vocabulary list, so candidates can name a softener or a corrosion inhibitor but cannot say what symptom it addresses, where it is installed, or what maintenance it needs.
What to do instead
Learn treatment as problem-solution pairs: symptom, cause, treatment, location, maintenance. Include the water quality parameters that indicate each problem (hardness, pH, chloride, conductivity) so you can interpret a given water analysis rather than just name a device.
When asked about handover, candidates mention 'giving the customer a certificate' but omit the wider handover package: commissioning records, test certificates, operating and maintenance instructions, benchmark or equivalent record, user instruction on controls, and the demonstration of isolation and safety devices.
Handover is treated as an administrative afterthought rather than a technical stage, so candidates underestimate how many distinct items the exam expects and lose marks across several small points.
What to do instead
Memorise handover as a checklist of categories: documentation, certification, labelling and identification, user demonstration, and maintenance information. Practise writing the checklist from memory and applying it to a specific installation type so the items are contextualised.
On fault diagnosis questions, candidates jump to a likely cause and describe the repair, skipping the systematic diagnostic sequence: gathering the complaint, confirming the symptom, isolating, testing in a logical order, and confirming the fault before replacing parts.
Experienced candidates recognise familiar symptoms and answer from pattern recognition, but exam scenarios often include a distractor symptom that makes the obvious cause wrong, and the marks are for the diagnostic process as well as the conclusion.
What to do instead
Answer every fault question with an explicit sequence: symptom and history, safe isolation, test points in order, interpretation of each reading, confirmed cause, then repair and re-test. State what a normal reading would have been so the reasoning is visible, and always include the post-repair verification step.