Heating working normally but no hot water at the taps is a useful symptom, because it rules out most of the things that would stop the boiler entirely.

What it points to depends on whether you have a combi or a cylinder.

If you have a combi boiler

The most common cause by some distance is the diverter valve. A combi sends heat either to the radiators or to the hot water, and the diverter valve decides which. When it sticks in the heating position, the radiators work perfectly and the hot water never gets any heat.

It is a repair rather than a replacement boiler, and it is a recognised wear item.

Less commonly it is the hot water thermistor, a blocked plate heat exchanger, usually from scale in a hard water area, or a flow sensor that is not registering that a tap has been opened.

If you have a hot water cylinder

Then the heating and hot water are two separate circuits, and the fault is usually in the hot water side of the controls.

• The cylinder thermostat has failed
• The zone valve for hot water has failed or is stuck
• The programmer is set to heating only, which is worth checking before anything else
• On an immersion, the element or its thermostat has failed

The check worth doing first

Hard water

In hard water areas, and Cambridgeshire and much of north Hertfordshire qualify, scale builds up in a combi plate heat exchanger and gradually reduces hot water performance before it stops it entirely. If your hot water has been getting slowly weaker for months rather than failing suddenly, that is the likely story.

How Vantage can help

Gas Safe registered, covering Hertfordshire, Bedfordshire and Cambridgeshire. Diverter valves and cylinder controls are routine work for us.

Frequently asked questions

Is a diverter valve expensive?

It is a repair rather than a new boiler. An engineer will confirm it is the valve before replacing it.

Why is my hot water lukewarm rather than absent?

Often a partially stuck diverter valve, or scale in the plate heat exchanger.

Could it be the thermostat?

On a cylinder system, frequently. On a combi, less often.

Does hard water cause this?

It contributes, by scaling the plate heat exchanger over time.

Want it sorted properly?

Anything past the free checks above needs a Gas Safe engineer with the right test kit. Ring Vantage on 01462 506374, any hour, any day of the year. You will get an honest arrival time rather than a comforting one, and the price before the work.

Where to next

• Boiler installation and repair
• Advice from our engineers
• Talk to a local engineer