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Hot water, but no heating can be disappointing, especially in the cold months. If the boiler gives you warm water but does not warm your radiator, do not worry – this problem is common and usually easy to fix.
Whether you’ve got a combi boiler, device boiler or oil boiler, this specific guide will assist you in recognizing what is happening, the way to remedy the issue, and whilst a professional has to call.
Why Is My Boiler Giving Me Hot Water but No Heating?
If the combi boiler does not warm the radiator, but heats the water, its technique is that the boiler works, but the primary heating stops running.This problem is common in many boilers, including Worcester, Valiant, Ideal, Ariston ,and others.
The problem usually lies in one of these key areas:
- A faulty diverter valve
- Issues with the thermostat
- Trapped air in the system
- Low boiler pressure
- Problems with the circulating pump
- A broken motorised valve (in non-combi systems)
Let’s go step by step to understand each of these and how to fix them.
1. Faulty Diverter Valve
A diverter valve tests if warm water from the Combi boiler goes into cranes or radiators.
If your combi boiler is powered however it no longer sends heat to the radiators, it may imply that the lacking valve is caught or damaged, allowing simplest warm water to waft from the faucet.
Signs of a Stuck Diverter Valve:
- You have hot water; however, no heating.
- The radiators live bloodless, despite the fact that the boiler is on.
- The boiler works excellently while warm water is turned on.
What You Can Do:
You’ll likely need a qualified heating engineer to inspect or replace the valve. This is not a DIY job unless you’re trained in boiler mechanics.
2. Thermostat Issues
Your room plays a big role in determining the boiler to heat the thermostat radiator.
- If your thermostat is inaccurate, sees too little, or is not speaking with the boiler, the radiators will now not be heated.
Troubleshooting phase:
- Make sure the thermostat is on and the temperature is higher than the room temperature.
- Change the battery if it is wireless.
- Reset the thermostat to see if it reconnects to the boiler.
- If the clever thermostat (eg, Hive or Nest) is used, take a look at your app and Wi-Fi connection.
If the combi boiler is hot however the radiators are bloodless, a short thermostat test might resolve your hassle.
3. Circulating Pump Issues
If the boiler fires up, but the radiators remain cold, the circulation pump may be incorrect.
The pump causes warm water from the boiler to the radiator. If jammed, broken, or air straps are used, do not transmit hot water.
Signs of a Faulty Pump:
- The boiler turns on but radiators stay cold.
- You hear no buzzing or vibration from the pump.
- The pump feels cold even when heating is on.
This issue usually requires a heating engineer to fix or replace the pump.
4. Motorised Valve Problems (Non-Combi Boilers)
If you don’t have a combi boiler and rely on a hot water tank, a motorised valve could be the issue.
This valve directs water either to the radiators, the water tank, or both. If it fails, you may get hot water but no heating.
This is a specialist job and you should call a professional if you suspect this is the issue.
5. Boiler Timer or Program Settings
Your heating can only be closed because the timer is incorrect, or the reset is required after a power cut.
Quick Solution:
- Check the boiler’s lesser/programmer.
- Make sure the heating is on.
- Confirm the correct date and time.
- If you use smart control, check the app settings.
6. Frozen Condensate Pipe (In Winter)
If it is too cold and your boiler has stopped heating, the capacitors can be frozen.
This plastic pipe moves from the boiler to the outer drain. If it accumulates, the kettle will be locked out.
How to Thaw It:
- Pour warm (not boiling) water over the pipe.
- Gently warm it with a hot water bottle or heat %.
- Restart the boiler.
Be careful not to damage the pipe.
7. Sludge Build-Up in Radiators
Over time, sludge and debris can build up inside your radiators. This can block hot water flow and reduce heating performance.
Symptoms:
- Some radiators are cold while others work fine.
- Radiators heat unevenly.
- Heating takes a long time to work.
Solution:
You may need a power flush, which uses high-pressure water and cleaning chemicals to clear the system. This must be done by a professional.
When to Call a Heating Engineer?
Some issues are simple and safe to fix. But in many cases, calling a qualified heating engineer is the safest and most effective route.
Call a professional if:
- You’ve tried all basic checks and the problem remains.
- The diverter valve, pump, or motorised valve needs replacement.
- You hear unusual noise from the boiler.
- Your boiler continues to lock or display the error code.
- You are not convinced to work with plumbing or gas units.
Trying to fix complex boilers can be dangerous in itself and can zero your warranty.
Common Boiler Brands: Tips for Troubleshooting
Let’s look at how some specific boiler brands may show this issue.
Worcester Boiler – Hot Water but No Heating
A stuck diverter valve is often the issue. Check pressure and bleed radiators first. If the heating still doesn’t work, the valve might need replacing.
Ideal Boiler – Hot Water but No Heating
Look at thermostat settings. If those are fine, check for low pressure or a frozen pipe.
Vaillant Combi Boiler – Hot Water but No Heating
Common issues are with the pump or diverter valve. Vaillant models often show error codes, so check your manual.
Ariston Boiler – Hot Water but No Heating
Ariston boilers may also suffer from diverter valve failure or air in the system. Try bleeding radiators first.
Conclusion
If your boiler is heating water but not radiators, you’re not alone. It’s a common problem with clear causes and proven fixes. Whether it’s a combi boiler not heating radiators, or your oil boiler gives hot water but no heating, the issue usually lies with:
- A stuck diverter valve
- A faulty thermostat
- Air trapped in radiators
- Low boiler pressure
- A broken pump
Start with the simple checks. If the issue persists, call a qualified heating engineer.
For ongoing peace of mind, consider booking an annual boiler service to prevent future issues.
Frequently Asked Questions
The maximum not unusual cause is a wrong diverter valve, thermostat troubles, constant air or low stress. If hot water works, however the beams remain bloodless, the valuable heating circuit may be blocked or won’t get a signal to start.
Start by checking:
- Boiler pressure
- Thermostat settings
- Whether radiators need bleeding
- If the timer/programmer is correct
If all seem fine, it may be time to call a professional.
In most cases, no. The diverter valve is placed within the boiler. Fixing or replacing it requires unique equipment and gasoline safety certification.
It could be a frozen condensate pipe or elevated call for inflicting low stress. Cold climate highlights small faults that move disregarded in warmer months.
Costs vary depending on the issue:
- Bleeding radiators: Free
- Pressure top-up: Free
- Thermostat replacement: £50–£150
- Diverter valve replacement: £200–£350
- Pump repair/replacement: £150–£300
Getting a quote from a Gas Safe engineer is always best.
