What to Do When Your Boiler Has No Hot Water

A cold shower is often the first sign that something is wrong, but a boiler without hot water does not always mean a major breakdown. If you are wondering what to do when boiler has no hot water, begin with a few safe, simple checks. Do not remove the boiler casing or attempt any gas work yourself. The aim is to identify whether the issue is something straightforward, such as low pressure or a setting, or whether it needs a qualified Gas Safe engineer.

For homeowners, landlords and managing agents, acting promptly matters. A lack of hot water can quickly affect tenants, families, care settings and day-to-day business operations, particularly during colder weather. Knowing what to check can also help you give an engineer a clearer description of the fault.

Start with the boiler display and controls

Look at the boiler's display panel first. Modern boilers often show a fault code, warning symbol or flashing light when they have locked out. Make a note of the code exactly as it appears, then check your boiler manual if you have it. The code can point to issues such as low system pressure, an ignition fault, a frozen condensate pipe or a circulation problem.

Next, check whether the boiler has power. Confirm that the fused spur beside the boiler is switched on and that no circuit breaker has tripped in the consumer unit. If the display is completely blank, it could be a power supply issue rather than a heating fault. Do not repeatedly reset electrical switches if they continue to trip - this needs investigation.

Check the programmer or smart thermostat too. Ensure hot water is set to ‘on’ or timed correctly, and that the clock has not reset following a power cut. If you have separate heating and hot-water controls, the heating may work normally while the hot-water setting has been turned off.

Check whether the heating still works

Whether your radiators are warming up is a useful clue. If you have heating but no hot water, the problem may be specific to the boiler's hot-water side. On a combi boiler, common causes include a stuck diverter valve, a faulty flow sensor, a plate heat exchanger blocked by limescale or sludge, or a failing temperature sensor.

If neither heating nor hot water is working, the cause may be broader. Low pressure, an ignition failure, a frozen condensate pipe, a gas supply issue or a boiler lockout are all possibilities. The exact diagnosis depends on the boiler model, its age and the fault information shown on the display.

Properties with a conventional or system boiler may have a different arrangement. If there is a hot-water cylinder, check that the cylinder thermostat is set appropriately and that the programmer is calling for hot water. A failed motorised valve, cylinder thermostat or immersion heater can stop hot water even where the boiler itself is operating.

Check the boiler pressure safely

Many sealed heating systems need pressure of around 1 to 1.5 bar when cold, although the recommended range can vary by manufacturer. The pressure reading may be shown on a dial or digital display. If it is below the minimum marker or close to zero, the boiler may refuse to operate.

Some boiler manuals explain how to repressurise using the filling loop or built-in filling link. Only do this if you are confident it is the correct procedure for your boiler and there is no visible leak. Add water slowly and stop at the manufacturer’s recommended pressure. Over-pressurising a system can create another problem.

Pressure that drops repeatedly is not something to keep topping up indefinitely. It can indicate a leak, a faulty pressure relief valve or an issue with the expansion vessel. A heating engineer should find the cause rather than simply restore the reading each time.

Reset the boiler once, not repeatedly

A reset can clear a temporary lockout, particularly after a brief interruption to the gas supply or power. Follow the instructions printed on the boiler or in its manual. Usually, this involves holding the reset button for a few seconds.

If it starts and stays running, keep an eye on the display and pressure over the next day or two. If it locks out again, do not continue resetting it. Repeated lockouts are a sign that the underlying fault remains and repeated resets can make diagnosis harder.

Look for an outside condensate pipe in freezing weather

Condensing boilers produce acidic water that drains away through a condensate pipe. In winter, an external pipe can freeze, causing the boiler to shut down. You may hear gurgling noises, see a lockout code or notice that the boiler stops shortly after trying to fire.

If the pipe is accessible at ground level and you can clearly identify it as the plastic condensate pipe, it can often be thawed carefully with warm water. Never use boiling water, a naked flame or any sharp object. Take care on icy paths and do not attempt to reach pipework at height.

Once thawed, reset the boiler once. If the pipe freezes frequently, it may need better insulation, rerouting or an upgrade to its installation. A properly assessed solution is safer than dealing with the same failure every cold spell.

When there is no hot water at one tap only

If hot water is absent from one tap or shower but works elsewhere, the boiler may not be the problem. A blocked tap aerator, failed shower cartridge, thermostatic mixing valve or local plumbing restriction can prevent hot water reaching a single outlet.

Try another hot tap in the property. If the kitchen tap runs hot but the shower does not, avoid adjusting the boiler pressure or resetting the appliance unnecessarily. A plumber can assess the affected fitting and identify whether the issue lies with the tap, shower valve or pipework.

Low flow is also worth noting. Combi boilers need a minimum water flow rate to detect a hot-water demand. If the cold water flow is very weak, the boiler may not fire consistently when a tap is opened. This is particularly relevant in properties with ageing pipework, partially closed stop taps or mains supply issues.

Safety checks you should never skip

If you can smell gas, suspect a gas leak or feel unwell with symptoms such as headaches, nausea or dizziness, leave the property if it is safe to do so. Do not use electrical switches, smoke, light a flame or try to repair the boiler. Call the National Gas Emergency Service on 0800 111 999 from a safe location, then arrange for a Gas Safe registered engineer to inspect the appliance.

A carbon monoxide alarm sounding is also an emergency. Open doors and windows if you can do so safely, leave the building and seek urgent advice. Carbon monoxide has no smell or colour, which is why an audible alarm and regular boiler servicing are so valuable.

Never take off your boiler cover, interfere with gas valves or attempt to replace internal parts. Boiler repairs involve combustion, electricity, water pressure and flue safety. What looks like a small part can affect the safe operation of the whole appliance.

When to call a Gas Safe engineer for no hot water

Call for professional help if the boiler shows a recurring fault code, has no power despite a working supply, loses pressure repeatedly, leaks, makes banging noises, or will not provide hot water after the basic checks above. You should also call if the boiler is old and unreliable, if a tenant is without essential hot water, or if you are unsure whether your system has a cylinder, immersion heater or combi boiler.

A qualified engineer can test the gas supply, combustion, sensors, pump, diverter valve, heat exchanger, controls and electrical components safely. The repair may be relatively minor, but only proper testing can establish that. In some cases, especially with an older appliance requiring costly parts, replacement may offer better long-term value. That decision depends on the boiler’s condition, repair history, efficiency and the needs of the property.

For homes and managed properties across Dartford, North Kent and South East London, PlumbTech365 can diagnose boiler and hot-water faults with clear communication, qualified Gas Safe workmanship and a practical focus on getting the property back to normal. Before an engineer arrives, keep the fault code, boiler make and model, and a brief note of when the problem began. Those small details can help turn a cold-water problem into a quicker, more accurate repair.