Maintenance, Fault Diagnosis and Repair
This domain tests systematic fault finding rather than parts swapping: gathering information, isolating, testing logically, repairing with the right component and proving the repair. Questions often describe a symptom and ask for the most likely cause or the next diagnostic step.
A diagnosis routine
- Take the customer's description and history. 2. Observe without dismantling. 3. Isolate the supply or drain. 4. Test each part of the system (open a nearby tap to prove supply). 5. Identify the fault. 6. Repair with the correct part. 7. Test, record and report.
Common faults and causes
- No water at one tap: blocked aerator, seized isolating valve, kinked flexible connector. Whole building: supply off, empty tank, pump failure, blocked main.
- Dripping tap: worn washer or ceramic cartridge, damaged seat.
- Cistern running into the pan: flush valve seal passing. Cistern overflowing outside: float valve set too high, or worn washer or seat. This distinction identifies the faulty valve.
- Water hammer: loose pipework, excessive velocity, failed float valve, no arrestor.
- Slow drain: partial blockage, wrong fall, grease, roots.
- Persistent smell: dry trap, blocked vent, leaking drain.
- Discoloured water: sediment in the tank, corroded galvanised pipe.
Preventive maintenance
Clean tanks about every six months, exercise stop valves, descale shower heads, check float valves, lubricate moving parts, keep an asset register and service history, and hold common spares.
Worked example
A WC runs continuously into the pan after flushing. First check whether water is also escaping down the overflow outside: it is not, so the float valve is fine. Water passing into the pan means the flush valve is not seating - clean the seal, remove scale, replace the diaphragm, and check the push button is not sticking. Reason: the overflow route tells you which valve is at fault, so you avoid replacing the wrong part.
Traps
- Replacing parts without a diagnosis and hoping the symptom stops.
- Dismantling before isolating the supply.
- Leaving scale or debris in the cistern so the new seal fails within days.
- Not testing the repair or recording what was done, so the fault returns unseen.