No hot water? Common causes and safe checks

Losing hot water is a pain, but the cause is often simple: a timer that reset after a power cut, a setting turned down, low boiler pressure or, in a cold snap, a frozen pipe outside. The checks below are safe for anyone to do. None of them involve opening the boiler or touching any gas parts.

Safety: If you smell gas, or think there could be carbon monoxide, stop. Open doors and windows, turn off the gas at the meter if you can, get everyone out into fresh air and call the National Gas Emergency Service on 0800 111 999. Don't use light switches or anything that could make a spark.

Do you have a combi boiler or a hot water cylinder?

The right checks depend on how your home heats water, so start here.

• Combi boiler: there's no hot water tank. The boiler heats water straight from the mains when you turn on a hot tap.
• System or regular boiler: the boiler heats a hot water cylinder, usually in an airing cupboard, and the water is stored until you use it. Many cylinders also have an electric immersion heater as a backup.
• Electric only: some homes, often flats, heat the cylinder with an immersion heater and no boiler at all.

Also notice whether the radiators still get warm. If the heating works but the hot water doesn't, the boiler is lighting, which narrows down the problem.

Does the boiler have power and gas?

Look at the boiler's display or lights. If they're blank, check other lights and sockets work in case there's a power cut, and that the switch next to the boiler is on. Look at your consumer unit too. If a breaker or RCD has tripped, switch it back on once. If it trips again straight away, leave it off and call a registered electrician.

If you have a prepayment or smart pay as you go gas meter, check you still have credit. If your gas hob also won't light, the problem is probably the gas supply rather than the boiler.

Is the timer or programmer set for hot water?

This is one of the most common causes with a cylinder, because the water is only heated at the times you set. Ideal Heating points out that timers can reset to their default settings after a power cut, and some fall out of step when the clocks change. Check that:

• The programmer shows the right time and day, including weekend settings.
• Hot water is switched on or set to a timed period, not off or set to heating only.
• The boiler isn't in standby, frost protection or a heating only mode.

If the cylinder has been used up, for example after several baths, give it time to reheat. Ideal suggests waiting about an hour.

Is the hot water temperature turned down?

Most boilers have a hot water temperature control on the front. If it has been turned right down, the water can feel cold. Ideal says water below 30°C will feel quite cold, especially in a bath.

If you have a cylinder, it may also have its own thermostat. Stored hot water should be kept hot. The Health and Safety Executive's guidance for rented homes says to set the cylinder so water is stored at 60°C, which helps control legionella bacteria. If you rent, don't change the cylinder setting yourself. Ask your landlord.

What should the boiler pressure be?

Combi and system boilers have a pressure gauge on the front. Ideal says it should usually read between 1 and 1.5 bar. If it's outside that range, the boiler may switch itself off for safety, which means no hot water.

Many manufacturers let you top the pressure up using the filling loop, following the steps in your boiler's manual. If you're not sure how, or the pressure keeps dropping, there may be a leak and it's a job for an engineer. Our guide to a boiler losing pressure has more detail.

No hot water in cold weather? Check the condensate pipe

Modern condensing boilers drain waste water through a plastic pipe, usually white, that runs outside to a drain. In freezing weather it can freeze and stop the boiler. Worcester Bosch says you may hear gurgling from the boiler and see a fault code on the display.

1. Find the plastic condensate pipe where it runs outside.
2. If it's safe to reach, pour warm water slowly along the outside section. Use warm water, not boiling.
3. Once it has thawed, reset the boiler as your manual describes.

Only thaw the outside plastic pipe. Never open the boiler casing. If no water comes out of any tap, hot or cold, the problem is the water supply, not the boiler. Your pipes may be frozen or your water company may have a supply problem in your area.

What if the immersion heater isn't working?

If you rely on an immersion heater, check its switch on the wall is on, that any immersion timer is set correctly and that its breaker hasn't tripped in the consumer unit. If the breaker trips again, or the switch or cylinder looks scorched or damaged, leave it off.

Don't open the immersion heater's cover or try to replace the element or thermostat yourself. It's wired to the mains, so any repair is a job for a registered electrician or a qualified plumber who does this work. Keep away from any electrics if the cylinder or airing cupboard is wet.

Heating works but no hot water?

If your radiators get hot but the taps don't, the boiler is lighting, so the fault is usually in the parts that send heat to your water. With a combi, Ideal says the diverter valve can stick. Turning the hot tap on and off a few times while the heating runs may free it. With a cylinder system, Ideal says the cause may be a zone valve that isn't working.

If that doesn't help, don't take anything apart. Valves, pumps and sensors need an engineer to diagnose and replace.

When to call a Gas Safe registered engineer

If you've done these checks and still have no hot water, book a professional. Anything inside a gas boiler, the gas pipework or the flue must be left to a Gas Safe registered engineer. Call one if:

• The boiler keeps locking out or showing a fault code after one reset.
• The pressure keeps dropping, or water is leaking from the boiler or its pipes.
• The boiler stays silent when you fully open a hot tap.
• You see soot, scorch marks or a yellow or orange flame instead of a blue one.

When the engineer arrives, ask to see their Gas Safe ID card. Check the photo matches the person, the card is in date and the back shows they're qualified for the work, such as domestic boilers. If you rent, report the problem to your landlord rather than booking an engineer yourself.