It’s frustrating to turn on a tap and get cold water while your radiators are perfectly warm. If you notice No hot water but heating works – what does it mean?, you’re not alone. This common issue occurs in many homes with combi boilers or system boilers. It often signals a problem specific to the hot water supply rather than the central heating circuit. Understanding the difference between heating and hot water circuits helps you diagnose the cause. Most problems are easy to fix, but some need a professional. In this guide, we break down why your heating works but your taps remain cold, the main culprits, and how to solve the problem safely.
How heating and hot water circuits work
Modern boilers separate the heating and hot water circuits. The heating circuit warms water for radiators or underfloor pipes, while the hot water circuit supplies taps and showers. Combi boilers heat water on demand using a heat exchanger. If one circuit works while the other doesn’t, it usually means the problem is in that specific path. For example, if radiators heat up but taps stay cold, the boiler can generate heat, but water cannot reach the taps or cannot flow through the domestic hot water coil. Knowing the separate pathways helps pinpoint whether the fault is in valves, sensors, or the heat exchanger.
Diverter valve problems
A common reason for No hot water but heating works – what does it mean? is a faulty diverter valve. The diverter valve controls whether hot water goes to radiators or taps. If it sticks in the heating position, all hot water goes to radiators, leaving taps cold. The valve can fail mechanically or get blocked by limescale. Symptoms include heating working normally while taps produce little or no hot water. In some systems, you may hear the boiler working harder when you turn on taps, indicating the valve is trying to switch. Fixing the diverter valve usually requires a professional, as cleaning or replacing it restores hot water without affecting heating.
Boiler thermostat or sensor issues
Your No hot water but heating works – what does it mean? can also involve boiler thermostats or sensors. Some boilers use separate thermostats for hot water and central heating. If the hot water thermostat fails, the boiler may not heat water even while radiators work. Similarly, temperature sensors on the hot water coil can misread or fail, preventing the boiler from activating the domestic hot water circuit. Checking the thermostat and sensors is a safe first step, but replacement usually requires a technician. Faulty sensors often show error codes on the boiler display or cause the boiler to run unusually.
Frozen or blocked pipes
If your No hot water but heating works – what does it mean?, consider frozen or blocked pipes. The hot water pipe leading from the boiler to taps may be blocked by debris or frozen in winter. Heating pipes, which often run internally or are larger, continue to work. Symptoms include one tap having no hot water while others remain functional, or no hot water anywhere. Carefully inspect exposed pipes for frost in cold weather. Thawing or clearing blockages restores flow. Always take precautions with frozen pipes to avoid damage or flooding.
Pump issues affecting hot water
In some systems, the pump moves water for both heating and hot water circuits. If the pump only circulates heating, hot water may not reach taps. This can happen if the pump’s diverter or multi-speed settings fail. Symptoms include radiators heating normally while taps have weak or no hot water. Checking the pump for faults or blockages may solve the problem. A trained technician can inspect the pump, adjust speeds, or replace worn parts to restore hot water.
Limescale and sediment buildup
A frequent cause of No hot water but heating works – what does it mean? in hard water areas is limescale or sediment buildup. The heat exchanger or domestic hot water coil can get clogged, reducing water flow. The heating circuit remains unaffected because the radiator loop often has cleaner water. Hot water flow may become weak or stop completely. Flushing the heat exchanger or treating the water system can resolve this issue. In older boilers, descaling or replacing the heat exchanger may be necessary to restore full hot water function.
Faulty plate heat exchanger (system boilers)
System boilers with a plate heat exchanger can develop leaks or blockages that lead to No hot water but heating works – what does it mean? The plate heat exchanger transfers heat from the boiler to the domestic hot water supply. If it leaks or clogs, hot water fails to reach taps, while central heating continues. You may notice a drop in boiler pressure or visible water under the exchanger. Fixing a faulty plate heat exchanger usually requires a professional because it involves draining the system, removing the boiler panel, and replacing or cleaning the exchanger.
Airlocks in the hot water system
Air trapped in pipes or the domestic hot water circuit can prevent flow. This causes No hot water but heating works – what does it mean? while radiators work fine. Airlocks are common after maintenance or system refills. Symptoms include gurgling sounds or hot water flowing intermittently. Bleeding the system or using simple air removal techniques can restore hot water. For multi-storey homes, airlocks may form in higher pipes. A professional can help remove stubborn air pockets safely without damaging the system.
Pressure-related causes
Boilers rely on sufficient pressure to circulate water. If the pressure is low, some boilers prioritize heating over hot water, causing No hot water but heating works – what does it mean? Pressure below the recommended range can also trigger error codes or stop the hot water flow. Check the boiler gauge, refill the system if needed, and monitor whether hot water resumes. Persistent low pressure suggests leaks, filling loop issues, or expansion vessel problems, which require professional attention.
Check for leaks in hot water circuit
Leaks in the domestic hot water loop can cause No hot water but heating works – what does it mean? while leaving the heating unaffected. Even small leaks reduce flow and prevent taps from reaching temperature. Look under sinks, near the boiler, and along exposed pipes for wet spots. Hidden leaks behind walls or floors may need a technician to locate. Fixing leaks restores water volume and ensures hot water reaches taps without affecting radiator heat.
Combi boiler quirks
For combi boilers, No hot water but heating works – what does it mean? often points to diverter valve issues or flow rate problems. Combi boilers heat water on demand, so low water pressure or restricted flow prevents the boiler from activating the domestic hot water mode. Heating continues because it uses the main circuit. Checking water pressure, ensuring valves are open, and clearing blockages can restore function. Professional servicing is recommended for complex combi boiler quirks.
Temporary system shutdowns or lockouts
Boilers have safety systems that prevent overheating or low water pressure. A temporary lockout may stop hot water while heating continues, giving the impression of No hot water but heating works – what does it mean? Causes include flame detection issues, blocked flues, or overheating in the hot water circuit. Resetting the boiler after troubleshooting is sometimes enough. Persistent lockouts need a professional to prevent repeated interruptions.
DIY checks before calling a professional
Before calling a technician for No hot water but heating works – what does it mean?, you can:
- Check boiler pressure and refill if needed.
- Ensure the hot water thermostat is set correctly.
- Make sure radiator valves are fully open.
- Listen for unusual noises indicating airlocks.
- Check for visible leaks or blockages in pipes.
These steps often reveal minor issues that are easy to fix or give information for a professional diagnosis.
When to call a professional
Call a professional immediately if:
- The diverter valve or heat exchanger may be blocked or faulty.
- You suspect leaks in hidden pipes.
- Airlocks persist after bleeding.
- The boiler shows repeated error codes.
Professional technicians have the tools and knowledge to safely inspect, repair, or replace parts. They can restore hot water without affecting the heating system.
Safety considerations
Even if your heating works, No hot water but heating works – what does it mean? should not be ignored. Failing components can worsen over time, leading to leaks, low pressure, or boiler lockouts. Handling hot water system components incorrectly can damage the boiler or cause flooding. Always follow safety guidelines and use trained professionals for complex repairs.
Energy efficiency impact
Hot water problems reduce energy efficiency. Boilers may run longer to try heating water that never reaches taps, wasting fuel. Resolving the issue restores normal circulation and ensures you get hot water quickly and efficiently. Proper maintenance also prolongs boiler life and keeps your home comfortable year-round.
FAQs about no hot water but heating works
Why do I have heating but no hot water?
Often, a diverter valve or heat exchanger issue prevents hot water flow while heating continues.
Can I fix this myself?
Minor issues like pressure or airlocks can be checked, but most diverter or heat exchanger faults need a professional.
Is it dangerous?
It is not immediately dangerous, but ignoring it can lead to leaks, lockouts, or boiler damage.
Why does my combi boiler heat radiators but not taps?
Low water flow, stuck diverter valves, or faulty sensors in combi boilers can cause this problem.
When should I call a professional?
Call a technician if DIY checks do not restore hot water, or if leaks, persistent error codes, or suspected valve issues exist.