Boiler not producing hot water? Common causes and what to do

Quick answer: If your boiler isn't producing hot water, common causes include low boiler pressure, incorrect control settings, a faulty diverter valve or a problem with the boiler's ignition or heating components. Some issues can be resolved through simple checks, but persistent hot water problems should be investigated by a qualified heating engineer.

Losing your hot water can be incredibly frustrating, especially when you need to shower, wash up or get the family ready in the morning.

Sometimes the heating works perfectly while the hot water stops completely. In other cases, both heating and hot water fail at the same time.

Understanding the symptoms can help you identify whether the problem is something straightforward or whether you need professional boiler repairs.

In this guide, Yorkshire Heating & Renewables explains the most common causes of hot water problems and what homeowners across Hull and East Yorkshire should do next.

What we cover

• Why boilers stop producing hot water
• What to check before calling an engineer
• Why heating can work without hot water
• Common faults with combi boilers
• When to arrange boiler repairs
• Frequently asked questions

Why is my boiler not giving me hot water?

There are several reasons why a boiler may stop supplying hot water.

The cause often depends on the type of boiler installed and whether the central heating is still working.

1. Low boiler pressure

Many modern boilers rely on the heating circuit maintaining the correct pressure to operate properly.

If the pressure drops below the manufacturer's recommended range, the boiler may stop working or display a fault code.

Most sealed heating systems typically operate at approximately 1 to 1.5 bar when cold, although the correct pressure varies between appliances.

Check the pressure gauge or digital display and compare it with the instructions for your boiler.

If your pressure keeps falling, read our guide on why your boiler keeps losing pressure.

Repeatedly topping up a system without investigating the cause can allow an underlying problem to continue.

2. Incorrect thermostat or programmer settings

Before assuming there's a fault, check your heating controls.

For boilers connected to a hot water cylinder, the programmer may be preventing the cylinder from heating.

Check that the hot water schedule is enabled and that the cylinder thermostat is set appropriately.

If you have a combi boiler, check that it hasn't been placed in an unsuitable operating mode.

3. Faulty diverter valve

A diverter valve is an important component in many combi boilers.

Its job is to direct heated water towards either the central heating circuit or the hot water heat exchanger, depending on demand.

If the valve becomes stuck or fails, you might find that:

• The radiators work but the taps produce cold water
• The hot water temperature fluctuates
• The boiler struggles to switch between heating and hot water

A faulty diverter valve usually requires professional diagnosis and repair.

4. Boiler ignition or burner problems

If the boiler cannot ignite properly, it may be unable to produce hot water or heat your radiators.

Potential causes include faults involving the ignition system, gas supply or internal safety controls.

Your boiler may display an error code to help identify the problem.

You should never attempt to remove the boiler casing, adjust gas components or repair internal parts yourself.

Gas boiler faults must be investigated by a Gas Safe registered engineer.

5. Problems with the hot water cylinder

If you have a system or regular boiler with a separate hot water cylinder, the fault may not be with the boiler itself.

Potential issues include:

• A faulty cylinder thermostat
• A malfunctioning motorised valve
• Incorrect programmer settings
• Problems with the cylinder's heating circuit

These faults can sometimes leave you with working radiators but insufficient hot water.

Why do I have heating but no hot water?

If the radiators are getting warm but the taps are running cold, the symptoms can help narrow down the possible problem.

With a combi boiler, a faulty diverter valve, flow sensor or another hot water component could be responsible.

With a system boiler, the problem may involve the cylinder controls, motorised valves or hot water programme.

The important thing is not to assume that your boiler needs replacing.

Many hot water faults can be repaired once the defective component has been identified.

Yorkshire Heating & Renewables provides boiler repairs for homeowners across Hull and East Yorkshire.

What should you check before calling a heating engineer?

There are several safe checks you can make before arranging a repair.

Check your boiler display. Look for an error code or warning message and refer to the manufacturer's instructions.

Check the boiler pressure. If you have a sealed heating system, make sure the pressure is within the recommended range.

Check your controls. Make sure the relevant heating or hot water programmes are enabled.

Try another hot tap. If only one tap is affected, the problem may be local to that outlet rather than the boiler.

Check whether your heating still works. Knowing whether the fault affects hot water, heating or both can help an engineer identify the problem.

Some manufacturers provide specific instructions for resetting a boiler following certain fault codes. Follow these instructions carefully and avoid repeatedly resetting a boiler that continues to fail.

Gas safety: If you smell gas, avoid using electrical switches, open doors and windows if safe to do so, leave the property and call the National Gas Emergency Service on 0800 111 999. If you suspect carbon monoxide, get into fresh air and seek urgent medical advice.

Should you repair or replace a boiler with no hot water?

Losing hot water doesn't automatically mean you need a new boiler.

If your boiler is relatively modern, has been maintained regularly and only requires a straightforward repair, fixing the fault may be the most cost-effective option.

However, replacement may be worth discussing if:

• Your boiler is approaching the end of its expected working life
• Breakdown frequency is increasing
• Replacement parts are becoming difficult to obtain
• Repair costs are significant compared with replacement
• The system no longer meets your household's heating and hot water requirements

If you're considering an upgrade, our new boiler installation service can help you explore the most suitable options for your property.

How can you reduce the risk of hot water problems?

Not every breakdown can be prevented, but regular maintenance can help identify developing faults before they become more serious.

Arranging an annual boiler service allows an engineer to check the appliance's condition, operation and safety.

It's also worth paying attention to early warning signs, including:

• Hot water taking longer to heat up
• Water temperatures changing unexpectedly
• Unusual noises from the boiler
• Frequent error codes
• Recurring pressure loss

If these symptoms continue, having the boiler inspected early may help prevent a more inconvenient breakdown.

Frequently asked questions

Why is my combi boiler running but there's no hot water?

A faulty diverter valve, flow sensor or hot water component could be responsible. The boiler may also be displaying an error code that indicates another problem.

Why does my hot water keep going hot and cold?

Fluctuating hot water can result from problems with water flow, temperature sensors, heat exchangers or other boiler components. A professional inspection is recommended if the problem persists.

Can low boiler pressure stop hot water?

Yes. Low pressure can prevent some boilers from operating correctly. Check the manufacturer's recommended pressure range and arrange an inspection if the pressure continues to fall.

Is having no hot water always a boiler fault?

No. Problems with taps, shower mixers, cylinder controls or external components can sometimes cause similar symptoms.

How much does it cost to repair a boiler with no hot water?

The cost depends on the cause, the boiler model and the parts or labour required. A professional diagnosis is the best way to establish the likely repair cost.

Should I replace my boiler if it keeps breaking down?

Repeated faults can indicate that replacement is becoming more economical, particularly with an older appliance. However, a heating engineer should assess its condition before recommending a new installation.

Need help with a boiler that has no hot water?

Whether your heating is still working or the entire boiler has stopped, the best approach is to identify the underlying problem before deciding on repairs or replacement.

Yorkshire Heating & Renewables provides professional boiler repairs, servicing and installations throughout Hull, Hedon, Beverley and the surrounding East Yorkshire area.

Our experienced local engineers can assess the problem, explain your options and recommend a suitable solution for your home.

Contact Yorkshire Heating & Renewables for professional advice or a free, no-obligation quotation.

Call 01482 947777 or get in touch.