Worcester boiler with no hot water

What it usually means

Worcester Greenstar boilers have a handful of features of their own that produce exactly this symptom, so it is worth going through those before reaching for the usual explanations. The most useful thing to establish first is whether the heating still works. Heating fine and no hot water puts the fault on the hot water side specifically, and on a combi that is a short and well-known list. Neither working is a different question about the appliance as a whole.

Start with the preheat setting, because it is Worcester's own and it changes the experience without changing anything mechanical. A Greenstar can be run in a comfort mode, where the boiler keeps its exchanger warm so hot water arrives quickly, or in an economy mode, where it waits until you actually draw water before firing. In economy the water genuinely takes noticeably longer to come through, and a household used to the other setting reads that delay as a failure. Switching between the two is a control setting rather than a repair.

Then look at the hot water temperature control itself. On several Greenstar models this is not marked in degrees but as a numbered scale, and it is entirely possible for it to have been knocked down to its lowest position — by cleaning, by a child, or by somebody adjusting the wrong dial. It produces water that is present and warm rather than absent, which is the version of this complaint most often misattributed to a failed part.

Next, the flow rate needed to make it fire at all. A combi only heats water when it detects water moving, and there is a minimum below which nothing happens. If a tap has scaled up, or a spray head or an aerator is partly blocked, the flow can fall under that threshold and the boiler will never light for hot water — the giveaway is that a full-bore bath tap works and a restricted basin tap does not. That is a two-minute check with a bucket and it eliminates the most expensive theories.

Only then the parts. Worcester publish a code specifically for a failed hot water temperature sensor, which produces the classic pattern of heating carrying on normally while hot water stops, and it is worth looking up because it names the fault outright. The other common mechanical cause on a combi is the valve that decides where the heat goes: stuck towards the heating circuit, you get hot water only while the heating is running, and stuck the other way you get radiators that stay cool. And in hard water areas the plate that transfers heat into your tap water scales up gradually, producing a decline over months rather than a failure on a particular day.

Two Greenstar specifics are worth knowing before you call. Models without a display use a blue light, and the way it flashes is the fault code — that pattern is worth writing down, because it is information nobody thinks to record. And if you have a Greenstar system boiler with a separate cylinder rather than a combi, most of the above does not apply: your hot water is made by a cylinder, a cylinder thermostat and a motorised valve, and those are the first three things to look at.