No hot water? What to check before calling an engineer

No hot water is frustrating, but the cause is not always a major boiler fault. A few safe checks can help you identify whether the problem relates to settings, pressure, ignition, the hot water cylinder or an electrical backup system.

The right checks depend on your heating system. Do not remove boiler covers or attempt gas, electrical or internal repairs yourself. If you notice a serious warning sign, stop and get professional help immediately.

Combi boiler checks

With a combi boiler, hot water is heated as you open a tap, so there is no separate cylinder. Start by checking whether the boiler display is on and whether other taps have the same problem. If only one tap is affected, a blocked outlet or tap fault may be responsible rather than the boiler.

Check the pressure gauge when the boiler is cold. Many systems operate somewhere around 1 to 1.5 bar, although the correct range varies by manufacturer, so use the installation or user manual as your guide. Very low pressure can prevent the boiler from operating, while repeatedly losing pressure suggests a fault that needs investigation.

• Check the boiler has power and that the controls are switched on.

• Look for a fault code or lockout symbol on the display.

• Confirm the gas supply is available, if other gas appliances are safe and working.

• Check whether the condensate pipe appears frozen, particularly during severe cold weather.

If the boiler is showing a lockout, you can usually try the reset procedure described in its manual. Reset controls differ between models, so do not repeatedly press the button or remove any panels. If it locks out again, arrange a boiler repair rather than continuing to reset it.

When heating works but hot water does not

If your radiators heat normally but the taps stay cold, the boiler has power and can produce heat, but the hot water side may have a problem. On a combi system, a faulty flow sensor, diverter valve or related control can stop hot water being delivered while the central heating continues to work.

A diverter valve directs heat either to the radiators or to the hot water circuit. It is not a homeowner repair, so note the symptoms and contact a qualified engineer if checking the controls makes no difference.

System boiler with a hot water cylinder

A system boiler works with a separate hot water cylinder, usually in an airing cupboard. Check the programmer or timer is set to provide hot water and that the cylinder thermostat has not been turned down too far. A typical hot water setting is around 60°C, but follow the manufacturer’s instructions and avoid making unnecessary adjustments.

Check whether the boiler fires when hot water is selected. If the boiler runs but the cylinder does not heat, the issue could involve a motorised valve, thermostat, pump or wiring. If the heating works but hot water does not, a control or valve problem is more likely than a complete boiler failure.

Some systems have a separate immersion heater for backup. Its switch is often located beside the cylinder or on a nearby wall. Check that it is switched on and that the relevant fuse or circuit has not tripped, but do not work on electrical components or investigate wiring yourself.

Using an electric immersion heater safely

An immersion heater heats water directly inside the cylinder and can provide hot water if the boiler is unavailable. Allow sufficient time for the cylinder to warm, then check whether the hot water becomes hotter. If the immersion switch is on but the water remains cold, the thermostat or heating element may have failed.

Never leave an immersion heater running continuously as a substitute for diagnosing a boiler or cylinder fault. If a fuse keeps tripping, there is a burning smell, or water is leaking from the cylinder, switch it off if safe and arrange an urgent inspection.

Urgent warning signs

Some situations should not wait for routine troubleshooting. If you smell gas, do not operate electrical switches, extinguish naked flames, open windows if safe, leave the property and contact the National Gas Emergency Service on 0800 111 999. If a carbon monoxide alarm sounds, leave immediately and seek emergency advice.

Water leaking near the boiler, cylinder or electrical controls is also a serious risk. Turn off the water supply or electricity only if you can do so safely, keep away from wet electrical equipment and call a qualified professional.

Information to provide when booking a repair

Make a note of your boiler make and model, any displayed fault code, the pressure reading and whether the heating still works. It also helps to explain when the hot water stopped, whether every tap is affected and whether the problem changes when you adjust the programmer or cylinder controls.

For repeated faults or an older boiler, replacement may be more practical than continued repairs. You can read more about boiler repair and boiler installation before making a decision.

If these checks do not restore your hot water, contact BeeExpress Heating & Renewables on 020 8970 7489. Providing the information above will help the engineer understand the fault and prepare for a safer, faster visit.