| Age of the system | Well within its expected life, with no history of trouble. | At or past the point most systems of its type get replaced. |
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| Nature of the fault | A component: element, thermostat, valve, pump, controller, thermocouple. | The cylinder itself leaking or corroded. Not repairable at any age. |
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| Repair history | First fault, or first in a long time. | Second or third repair in a short period. Components age together. |
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| Parts availability | Parts current and readily obtainable. | Model no longer supported, or parts on long lead times. |
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| Cost of the repair | Small relative to a replacement, on a system with life left. | Approaching a meaningful share of a new system's installed cost. |
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| Whether it suits the household | Capacity and recovery still match how the hot water gets used. | Already running out, or the household has grown since it went in. |
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| Running cost | Already an efficient system for the property. | Old electric storage where a heat pump would materially reduce running cost. |
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| Warranty position | Still under manufacturer warranty for the failed part. | Out of warranty, with no support to fall back on. |
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| Urgency | A repair restores hot water today with parts on the van. | Not urgent, so there is time to choose properly rather than take what is available. |
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| Planned work on the property | No renovation or change planned. | Bathroom or extension coming, which changes demand and may move the system anyway. |
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