General maintenance for your water heater

"Water heater" is an American phrase for a British set of three different machines, and the first useful thing this sheet can do is work out which one is in your house, because their maintenance is not just different in cost, it is different in what the rules expect. The three: the combi boiler (heats hot water on demand, no tank); the vented cylinder (the copper tank in the loft feeding it, hot water stored in an airing-cupboard cylinder, often with an electric immersion heater); and the unvented cylinder (a mains-pressure sealed cylinder, white and factory-insulated, usually taller than it is wide). Each has its own section below, and the third one has a service expectation the other two do not.

The combi: the annual service is the maintenance

A combi's water-heating side is looked after by the same service as its heating side: the annual boiler service, which covers the burner, the heat exchanger, the flue gas route, the pressure, and the little filters and sensors that decide whether your hot water arrives at full strength or as a disappointed trickle. Arrange it with a Gas Safe registered engineer and confirm what the service includes for your model. Between services, your maintenance is watching: the pressure dial cold (as in our pressure sheet), limescale on the shower head rather than in the boiler, and any change in how long the hot tap takes to warm. In hard-water areas, the combi's hot water plate heat exchanger is the part that furs first, and a common symptom is hot water that runs cooler when two taps open at once.

The vented cylinder: gravity-fed, and honest about its faults

The vented system's maintenance list is short and physical. The immersion heater (if fitted) has its own thermostat and can fail in two directions: dead cold, or, the one that matters, stuck heating, where a cylinder runs scalding and discharges very hot water through the overflow. If your immersion trips its cut-out, treat that as a fault to have looked at, not a button to keep pressing. The loft tank needs its lid on, its float valve working, and a jacket; open water tanks collect dust, limescale and the occasional insect, and what lands in the tank lands in your hot water. The cylinder thermostat should hold stored water hot enough to keep legionella from colonising the store, without making every tap in the house a scald risk. Stored hot water temperature is set in the cylinder thermostat, and the right figure depends on your cylinder and any thermostatic mixing valve; the manufacturer's instructions are the place to confirm it rather than a generic number. And drain a bucket from the cylinder's drain-off once a year if accessible: a cupful of brown grit will tell you the system is producing sediment.

The unvented cylinder: the one with a law in it

An unvented cylinder holds mains-pressure hot water in a sealed vessel, which makes it a superb performer and, if neglected, a pressure vessel. For that reason, unvented cylinder work is treated as specialist work: installation, and any maintenance or repair that touches the safety components, should be done by someone competent in that specific work, and the manufacturer's installation and service instructions set out the checks your model expects. Those checks will differ by make and model, but typically cover the safety valves, the expansion vessel, and the discharge pipework. This is not an upsell; it is the basis on which the safety design of the appliance rests. If you own an unvented cylinder and it has not been looked at this year, that is the phone call this sheet exists to prompt. Ask your installer or the manufacturer what interval your model needs, and keep a dated service label tied to the pipework, where the next person will find it.

The checks common to all three

Whatever stores or makes your hot water: know where it isolates (cylinder cold feed valve, or the combi's filling and isolating valves), feel the pipes and flanges for weeping once a season, a damp cylinder cupboard is a slow leak announcing itself, keep the airing cupboard door able to open fully, and keep every storage box in the house away from the flue, the discharge pipe, and the electrics. None of these need a plumber; they need someone to look, occasionally, on purpose. If a pipe fitting is weeping, a gentle quarter-turn on a compression nut while holding the body steady is the usual first step, but do not force seized or corroded parts. A hard-water area will scale immersion elements and heat exchangers faster than a soft-water one, so scale-related symptoms, noisy kettles, slow hot water, are worth noting by location rather than treating as universal.

What this sheet does not cover

This sheet has not covered solar thermal coils, heat pumps, or thermal stores, each is its own machine with its own service regime, nor the electrical side of immersion circuits beyond the safety notes above. Water temperature and scald protection for young children or vulnerable adults (TMVs on outlets) is a fit-for-the-household decision that is better discussed with a qualified plumber than settled in a general sheet. And if your hot water comes from something older than anything described here, the honest first step is a look by someone competent, not a manual.