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No Hot Water? What to Check and When to Call an Engineer

Homeowner checks a kitchen tap beside a boiler

If you have no hot water, start with the simple things: a power cut, an empty prepayment meter, hot water switched off on the boiler or programmer, and any error message on the boiler display. If none of those explains it, the fault is almost certainly inside the boiler or cylinder, and that is a job for a Gas Safe registered engineer, not for you. Below you will find the checks that are safe to do, what each symptom usually means, and what your rights are if you rent.

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TL;DR

  • Check power, prepayment credit, the hot water setting and the boiler display first. These take five minutes and need no tools.
  • Heating works but taps run cold? A stuck diverter valve is a common cause, and it needs a Gas Safe registered engineer.
  • Never open up a gas boiler or try to repair it yourself. If you smell gas, ventilate and call 0800 111 999.
  • Renters: tell your landlord straight away, in writing. Landlords must keep heating and hot water installations in working order.
  • Still cold after the basic checks? Book an engineer rather than waiting for the fault to get worse.

Table of Contents

Start here: the five-minute checks

Before assuming the boiler has broken, rule out the causes that cost nothing to fix. Citizens Advice lists the usual suspects for a sudden loss of hot water: a power cut, insufficient prepayment credit, hot water switched off, a boiler fault or pilot light that has gone out, a frozen condensate pipe, or a cylinder that has simply run out.

Work through them in this order:

  1. Power. Are the lights on? Is the boiler display lit? Check whether the fused spur or socket supplying the boiler is switched on.
  2. Prepayment credit. If you have a prepayment gas or electricity meter, check there is credit and emergency credit has not run out.
  3. Hot water setting. Look at the boiler and the programmer or thermostat. Is hot water switched on, and is the timer window correct for the time of day and day of the week?
  4. Boiler display. Note any warning or error code and look it up in the manufacturer’s guide. Write it down, because an engineer will ask for it.
  5. Other taps. Run the hot tap in the kitchen and the bathroom. If only one outlet is cold, the fault may lie with that tap or shower rather than the boiler.

Citizens Advice is clear on one point: do not try to fix the boiler yourself. Everything above involves switches and settings only.

What the pattern tells you

“No hot water” can mean several different things, and the pattern narrows down the cause quickly.

What you notice Likely area to look at What to do
Heating works, taps run cold Diverter valve, or hot water setting Check settings, then call a Gas Safe registered engineer
Nothing works, display blank Power supply or prepayment credit Check meter and fused spur
Only one tap or shower is cold That outlet, its mixer or cartridge Test other taps; call a plumber
Hot water runs out quickly Cylinder size, heating time or immersion Check timer and cylinder settings
Boiler shows a fault code or has switched itself off Pressure, ignition or a safety lockout Check the manual, then call an engineer
No water at all from the hot tap Mains water supply problem Check the cold tap and ask neighbours

This matters because a symptom that looks like a boiler failure is not always one. If all your outlets run cold, you may have run out of hot water or the boiler or cylinder may not be working properly. If only one outlet is affected, that tap or shower is the first place to look.

Heating works but there is no hot water

This is the version of the problem most people search for, and it has a well-known suspect. On a combi or system boiler, a diverter valve directs heated water either to the radiators or to the taps. When it sticks in the heating position, the radiators get warm and the taps stay cold.

Uswitch names a faulty diverter valve as a possible cause when heating works but hot water does not, and says that repair requires a Gas Safe registered engineer. The valve sits inside the boiler casing, so it is not something to investigate with a screwdriver.

What you can do before the engineer arrives:

  • Confirm that hot water is switched on at the boiler and the programmer.
  • Run a hot tap for a minute. On a combi boiler, Citizens Advice recommends checking that the boiler’s hot water setting is at least 50°C and trying the eco or pre-heat settings where fitted.
  • Note whether the problem is constant or comes and goes. Intermittent hot water is itself a sign worth reporting.

If the boiler is old and the diverter valve is one of several recurring faults, it can be worth asking whether repair still makes sense. Our boiler installation service covers replacement when that is the better route.

Cold water works, hot does not

If cold taps are fine and the hot side is dead, think about what produces your hot water.

Combi boiler. There is no tank. The boiler heats water as you open the tap, so a boiler fault, a setting or low pressure affects hot water straight away.

Cylinder (hot water tank). Here the water is stored. Citizens Advice says a cylinder probably needs heating for one or two hours before use, depending on its size and insulation. If your timer window has shifted, for example after a power cut reset the clock, you may simply have an unheated tank. The same page notes that an immersion heater can provide extra hot water for a short time, but it is expensive to run, so treat it as a stopgap.

Hot-water cylinder inside an airing cupboard

No water at all from the hot tap. If nothing comes out, rather than cold water, the issue may be with the water supply, such as roadworks or frozen pipes. System and combi boilers need water pressure to deliver anything. Check the cold kitchen tap and ask a neighbour.

Boiler checks that are safe to do yourself

A useful rule: if the check needs no tools, no electrical work and no removing covers, it is reasonable to do it. If it does, stop.

The oil-heating trade body OFTEC takes the same line in its consumer troubleshooting advice. It says users can check fuel, electrical supply, programmer time and day, thermostat and system pressure without tools or working at height, and should seek a technician if they are unsure. It adds that on a combi or sealed system, pressure below 0.5 bar may need topping up following the boiler instructions, and that a burner lockout should not be reset more than twice. That advice is written for oil-fired appliances, so for a gas boiler follow your own manufacturer’s manual and call a Gas Safe registered engineer if anything is unclear.

Practical notes:

  • Pressure. Look at the gauge. Low pressure often follows a small leak or recent bleeding of radiators. Your manual shows the correct range and the filling procedure for your model.
  • Frozen condensate pipe. In cold snaps, the plastic condensate pipe outside can freeze and shut the boiler down. The Citizens Advice page above lists it as a cause of sudden loss of hot water. Do not pour boiling water over it without following your boiler’s guidance; if you are unsure, call an engineer.
  • Pilot light. Older boilers have one. If it has gone out, relight it only if the manual describes how and you are comfortable doing so. Repeated failures mean a fault.

Never remove the boiler casing, adjust gas valves or bleed gas lines. That is not a limit on what is sensible; it is the law, as the next section explains.

Why a Gas Safe registered engineer matters

The Health and Safety Executive states that gas work must be done by a Gas Safe registered engineer under the Gas Safety (Installation and Use) Regulations 1998. In a 2026 HSE case, a man was sentenced after illegal gas work put a family at risk, and the HSE explains that unqualified work can cause gas leaks, fires, explosions and carbon monoxide poisoning.

Gas Safe Register lists pilot light failure, a boiler switching itself off, pressure loss, leaks, kettling and intermittent heat or hot water as signs of a boiler problem. Its advice is to contact a Gas Safe registered engineer if you have concerns, and to have the boiler serviced regularly. If you are not sure when yours was last checked, our guide to the gas safety check explains what it covers and who needs one.

Ask to see the engineer’s Gas Safe ID card before they start work. Our engineers are Gas Safe registered, and our gas works page explains what we handle.

If you smell gas

Stop troubleshooting. Gas Safe Register’s emergency advice is to get fresh air, open doors and windows, avoid naked flames and electrical switches, turn off the emergency control valve if it is safe to do so, and call the emergency service. For natural gas in England, Wales and Scotland, that number is 0800 111 999.

Steps to take if you smell gas

A no hot water problem and a gas smell together should be treated as a gas emergency first and a plumbing problem second.

Perspective: what we see when hot water fails

Most calls about no hot water begin the same way: someone has tried to do too much, or too little. Some people wait several days hoping it will come back, while the fault, a stuck valve or a pressure leak, gets worse. Others open the boiler casing and make a repairable fault into an unsafe one.

Our advice is a middle path. Do the five-minute checks, write down what you see, and then get an engineer who can diagnose and fix the fault on the same visit. We work to fixed-price quotes agreed before work starts, so you know the cost before anything is done, and our Gas Safe registered engineers cover boiler and gas faults across London, around the clock.

The other thing we stress is that a cold shower is rarely just an inconvenience. In winter it can mean a household with young children or an older relative without safe washing water or heating. That is why we answer calls 24/7 and treat a failed boiler as urgent.

the author

Renting: how long can you be left without hot water?

There is no single number of days that applies everywhere, but the law and official guidance point in the same direction: heating and hot water faults are urgent.

  • Landlord’s duty. Shelter England explains that section 11 of the Landlord and Tenant Act 1985 requires landlords to keep installations for heating and hot water in repair and proper working order, including boilers, central heating and the relevant pipes. It also says these failures are often emergencies, and that what counts as reasonable time depends on circumstances such as the season.
  • Tell your landlord. Citizens Advice says tenants should report a boiler failure to the landlord, who is responsible for repairing or replacing it. Tenants should not attempt boiler repairs themselves.
  • Council guidance. Lambeth Council advises reporting a lack of heating or hot water immediately by phone and following up in writing. It says landlords should normally attempt serious hazards such as a broken boiler within one to three working days. For non-emergency repairs, Wigan Council says 14 days should usually be considered reasonable, while serious hazards may need faster action.
  • Council and housing association tenants. Under the Right to Repair scheme, qualifying heating or hot water failures should be addressed within one working day from 31 October to 1 May, and within three working days from 1 May to 31 October.
  • Social landlords. GOV.UK guidance on Awaab’s Law, published on 31 July 2026, says a reasonable social landlord may need to make an emergency hazard safe within 24 hours, including by providing temporary heaters while a boiler is fixed. It is written for social landlords and does not replace their wider section 11 duties.

If you live in a building with a communal system, the rules differ. Citizens Advice says heat network users should contact their landlord or heat network supplier, and the supplier should contact affected customers or the landlord about an outage within 24 hours.

Keep a record: dates you reported the fault, who you spoke to, and photos of any error codes. These matter if you need to escalate to the council.

If you are the landlord

A broken boiler is your repair, and delay is costly for you and your tenant. Act on the report the same day, arrange a Gas Safe registered engineer, and keep records of the visit. A landlord who responds quickly avoids disputes, damp from unheated rooms and escalation to the local authority. Our emergency call out service is built for exactly this, and the 24 hour plumber guide explains what to expect when you call.

Could it be a leak or a pipe problem?

Not every hot water failure is the boiler. Pressure that keeps dropping can point to a leak in the heating circuit, and a damp patch, a hissing sound or a rising water bill suggests water is escaping somewhere. Pipe faults, a blocked or frozen pipe, or an airlock can also leave taps running poorly. If you suspect a hidden leak, our leak detection team finds the source without tearing up floors unnecessarily, and our plumbing work service handles the repair of taps, mixers, cylinders and pipework.

Book an engineer without the guesswork

If the checks above have not brought the hot water back, you do not need to keep experimenting. Our engineers answer calls 24/7 across London, and every job is quoted at a fixed price before work starts, so there are no surprises when the work is done. You pay on completion.

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For a boiler that has failed for good, see our boiler installation page. For anything urgent tonight, go straight to the emergency call out page, or browse all plumbing services in London.

Keeping hot water reliable

A few habits cut the odds of an unpleasant surprise:

  • Annual service. Gas Safe Register recommends regular servicing, and a service is often when worn parts are spotted before they fail.
  • Know your boiler. Keep the manual, learn where the pressure gauge and display are, and know what normal looks like.
  • Check timers after power cuts. Many programmers lose the time and need resetting.
  • Protect against frost. Insulate exposed pipes and the condensate pipe before winter.
  • Act on early signs. Intermittent hot water, odd noises and a boiler that switches itself off are warnings, not quirks.

FAQ

Why do I suddenly have no hot water?

The commonest causes are a power cut, an empty prepayment meter, hot water switched off at the boiler or programmer, a boiler fault or pilot light failure, a frozen condensate pipe, or a cylinder that has run out. Check the simple ones first. If the boiler shows a fault code or the problem continues, call a Gas Safe registered engineer.

Why do I have no hot water but the heating is working?

A diverter valve stuck in the central heating position is a likely cause, because it sends heated water to the radiators instead of the taps. Check that hot water is switched on and the timer is correct. If it is, the valve needs repair or replacement by a Gas Safe registered engineer.

Why is my hot water not working but cold water is?

If every hot outlet is cold, the boiler or cylinder is the likely source. If just one tap or shower is affected, the fault is probably with that outlet. Try several taps to tell the difference before you call anyone.

How long can a landlord leave me without hot water?

There is no fixed number for every tenancy, but landlords must keep heating and hot water installations in working order. Shelter says failures are often emergencies, and Lambeth Council says landlords should normally attempt a broken boiler within one to three working days. Report it at once and follow up in writing.

Can I fix a boiler that is not producing hot water myself?

Only the safe checks: power, credit, settings, display codes and, where your manual explains it, pressure. Anything inside the boiler is gas work and must be done by a Gas Safe registered engineer. If you smell gas, ventilate and call 0800 111 999.

Sources

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