No Hot Water? Quick Checks & When to Call a Pro

By The FixDelivered Team · Updated 2026-07-05 · 7 min read

Waking up to no hot water can be a real headache, especially on a chilly British morning. Before you panic and reach for the phone, there are several straightforward checks you can perform yourself. This guide will walk you through diagnosing common issues with combi boilers, conventional boilers with cylinders, and immersion heaters, helping you understand when a simple fix might be possible and, crucially, when it’s time to call in a professional.

Understanding Your Hot Water System

Knowing what type of hot water system you have is the first step in troubleshooting.

Combi Boiler: A combination boiler provides hot water on demand without needing a separate hot water cylinder. It heats water directly from the mains when you open a hot tap.
Conventional (Regular) Boiler with Hot Water Cylinder: This system uses a boiler to heat water, which is then stored in a hot water cylinder, typically in an airing cupboard. It requires a cold water storage tank (usually in the loft) and a feed and expansion tank.
Immersion Heater: Often found in conventional systems as a backup, an immersion heater is an electric heating element submerged in your hot water cylinder. It heats the water electrically, independent of your boiler.

Initial General Checks for No Hot Water

Before delving into specific system checks, rule out these common culprits:

Check Your Power Supply: Has a fuse tripped or an RCD (Residual Current Device) activated in your consumer unit (fuse box)? Reset any tripped switches. If it trips again, there’s an electrical fault that needs attention from a qualified electrician.
Is Your Gas Supply On? If you have a gas boiler, check that the gas supply valve to your property (usually near the meter) is open. Ensure other gas appliances (like your hob) are working. If you suspect a gas leak or smell gas, turn off the supply immediately, open windows, and call your gas network emergency number. Do NOT attempt to fix it yourself.
Is Your Water Supply On? Check your mains stopcock (usually under the kitchen sink or near the front door) is fully open.
Are Your Thermostats Set Correctly? Ensure your room thermostat and hot water thermostat (if you have a cylinder) are set to a comfortable temperature and not turned right down.
Check Your Timer/Programmer: Is your hot water set to come on at the correct time? It's surprising how often this is the issue after a power cut or accidental adjustment.

Troubleshooting a Combi Boiler with No Hot Water

If you have a combi boiler and no hot water (but heating might still work), try these steps:

Check the Boiler Display: Look for any error codes or fault lights. Make a note of the code – this will be very helpful if you need to call a plumber.
Check the Boiler Pressure: Most combi boilers have a pressure gauge, usually on the front panel. It should typically read between 1 and 1.5 bar when the system is cold. If it's below 1 bar, you may need to repressurise your boiler. Refer to your boiler's manual for instructions on how to do this safely using the filling loop.
Reset the Boiler: Many issues can be resolved by simply resetting the boiler. There's usually a reset button or dial – hold it down for a few seconds as per your manual.

When to Call a Professional for a Combi Boiler:

If you see any error code you can't resolve with a simple reset or repressurisation.
If the pressure drops repeatedly after repressurising.
If the boiler makes unusual noises, smells gas, or has a leak.
If the boiler is firing but not producing hot water, or the hot water is only lukewarm.
Any work on the internal components of a gas boiler must be carried out by a Gas Safe registered plumber.

Troubleshooting a Conventional Boiler with Hot Water Cylinder

If your boiler heats a separate hot water cylinder, check these points:

Is the Boiler Firing? Check if your boiler is actually turning on and heating water when hot water is called for by your programmer.
Check the Cylinder Thermostat: This is usually a small dial on the side of your hot water cylinder. Ensure it’s set to at least 60°C to kill legionella bacteria.
Check the Motorised Valve: If you have one, this valve directs hot water from the boiler to either the radiators or the hot water cylinder. Sometimes it can get stuck. You might hear a whirring sound when it operates. If it's stuck in the heating position, it won't send hot water to your cylinder. Some valves have a manual override lever – check your manual.
Consider the Immersion Heater: If your boiler isn't working, you might be able to use your immersion heater as a backup. See the section below.

When to Call a Professional for a Conventional System:

If the boiler isn't firing at all, or is firing but not heating the water in the cylinder.
If the motorised valve is stuck and you can't manually override it, or it's making unusual noises.
If you suspect a problem with the boiler itself (leaks, strange noises).
As always, for gas boiler issues, contact a Gas Safe registered plumber.

Troubleshooting an Immersion Heater

If your hot water comes solely from an immersion heater, or you're using it as a backup:

Check the Fuse Spur Switch: Immersion heaters typically have a dedicated switch on the wall near the cylinder. Ensure it's switched on.
Check Your Consumer Unit: As with the general checks, ensure the RCD or fuse for the immersion heater hasn't tripped.
Check the Thermostat: Immersion heaters have a thermostat, often located under a small cover on the top of the heater. Ensure it's set correctly. Be cautious when removing covers – if in doubt, switch off the power at the consumer unit first.

When to Call a Professional for an Immersion Heater:

If there's no power to the immersion heater even after checking switches and fuses.
If the water is still cold after several hours of the immersion heater being on.
If you hear unusual sounds from the cylinder or smell burning.
Working with electricity, especially high-power appliances like immersion heaters, can be dangerous. If you're unsure, call an electrician or a plumber.

Typical Costs for Hot Water Repairs (2026 UK Guide)

The cost of fixing no hot water varies significantly depending on the issue, your location, and the type of plumber you call (e.g., emergency vs. standard). As a rough guide for 2026:

Standard call-out/first hour: Typically £80 - £120.
Emergency call-out: Can range from £120 - £200+ for out-of-hours or bank holiday work.
Repressurising a boiler (if a plumber does it): £80 - £120.
Replacing a minor boiler part (e.g., pressure sensor, thermistor): £150 - £300 (including part and labour).
Replacing a motorised valve: £200 - £400.
Replacing an immersion heater element: £150 - £300.

Always get a clear quote before any work begins. Many plumbers will charge a call-out fee which includes diagnosis.

When to Always Call a Professional Plumber

While DIY checks can save you time and money, some situations absolutely require a qualified professional:

Any Gas-Related Issue: If you suspect a gas leak, smell gas, or your gas boiler is making strange noises or has an error code you can't fix, immediately call a Gas Safe registered plumber. Never attempt to work on gas appliances yourself.
Persistent Boiler Faults: If your boiler keeps locking out, losing pressure, or failing to ignite.
Leaks: Any water leak, especially from a boiler or cylinder, needs immediate professional attention to prevent damage.
Electrical Faults: If fuses are tripping repeatedly or you suspect an electrical issue with your immersion heater.
Lack of Confidence: If you're unsure about any step, or uncomfortable working with appliances or electricity, it's always safer to call a professional.

Get a Vetted Local Plumber Fast

When you need professional help, FixDelivered can connect you with vetted, local emergency plumbers quickly. Our platform simplifies the process of finding a reliable tradesperson, ensuring you get transparent pricing and quality service. You can how FixDelivered works to see how easy it is to find help.

Don't let a lack of hot water disrupt your day. If your DIY checks don't resolve the issue, tell us your emergency and get a trusted plumber on their way. The booking fee is refundable if no plumber is found, and the plumber's callout fee is agreed upfront and paid directly to them, ensuring no nasty surprises.

Frequently asked questions

Why is my hot water not working but heating is?

This often points to an issue with the diverter valve in a combi boiler (which directs hot water to taps or heating), or a fault with the hot water cylinder's thermostat or motorised valve in a conventional system. Check your boiler's display for error codes or your cylinder's programmer settings.

How long does it take for hot water to come back after a power cut?

For a combi boiler, hot water should be available almost immediately once power is restored and the boiler has reset. For a conventional system with a hot water cylinder, it depends on the size of your cylinder and the boiler's output, but typically it can take 30-60 minutes to heat a full tank of water.

What should I do if my boiler keeps losing pressure?

If your boiler frequently loses pressure, it indicates a leak somewhere in the system or a faulty pressure relief valve. While you can repressurise it yourself in the short term, a persistent drop in pressure requires investigation by a <a href="/gas-safe-plumbers">Gas Safe registered plumber</a> to find and fix the underlying cause.

Can I use an immersion heater if my boiler breaks down?

Yes, if your conventional system has a working immersion heater, you can typically use it as a backup to heat your hot water cylinder electrically. Just ensure the immersion heater switch is on at the wall spur and check your consumer unit. Be aware it's generally more expensive to run than a gas boiler.

Need a plumber now? Tell us your emergency and FixDelivered will find and confirm an available local plumber near you, usually within the hour.

Written by the FixDelivered Team. Reviewed by Rupert Lowe, Editor. Last updated 2026-07-05.