No Hot Water But Heating Works? Here's What's Usually Wrong

It's one of the odder faults: radiators toasty, taps stone cold. On a combi boiler there's a short list of likely culprits.

The diverter valve A combi sends hot water either to your radiators or to your taps, and a diverter valve decides which. When it sticks in the heating position, you get heating and no hot water. It's a very common failure and usually a repair rather than a replacement boiler.

Plate heat exchanger scaled up The secondary heat exchanger transfers heat to your tap water. In hard water areas it scales up and hot water becomes lukewarm and slow, often before it fails completely.

Thermistor or flow sensor If the boiler can't sense water flowing when you open a tap, it never fires for hot water. Cheap part, quick fix, but it needs diagnosing properly.

Cylinder systems If you have a hot water cylinder, look at the motorised valve, the cylinder thermostat and the immersion heater. A failed two-port valve is the classic — and it's the exact job customers have called us out for across Cardiff many times.

Don't guess at parts Boiler parts are expensive to buy wrongly. A proper diagnostic visit costs less than a mis-ordered heat exchanger.

Lost hot water in Cardiff? Call PHBLUE on 07545 125168.