If your heating is not working but the hot water is, check the room thermostat, the heating timer and the boiler pressure first. Those three cause a lot of cold radiators on their own. If they’re all fine, a combi’s diverter valve may be stuck on hot water, or on a system boiler the heating zone valve or the pump has failed. Have it the other way round, with warm radiators and cold taps? Read our guide to heating but no hot water.
We’re Clever Energy Boilers, Gas Safe registered (no. 554138) and accredited Worcester Bosch installers based in Bingley. We’ve fitted more than 25,000 heating systems across Yorkshire, the North West and the Midlands, and this is one of the heating questions we hear most in winter.
Heating not working but hot water is: what should I check first?
- Room thermostat: turn it a few degrees above the current temperature. Swap the batteries if the display is faint or blank.
- Heating timer: make sure the heating channel is on, not just the hot water. Try the “advance” or “boost” button.
- Smart thermostat: check it’s online and still paired with the boiler. Our guide to smart thermostats has more on how they connect.
- Boiler pressure: the gauge should read at least 1 bar. If it doesn’t, here’s how to repressurise a boiler.
- Radiator valves: make sure the thermostatic valves aren’t turned down to zero.
Why does my combi boiler have hot water but no heating?
Is the diverter valve stuck on hot water?
The diverter valve switches the boiler’s output between your taps and your radiators. If it sticks in the hot water position, you’ll get perfectly good showers and cold radiators. It’s one of the commonest combi faults. Our guides on a faulty diverter valve and freeing a stuck diverter valve explain the symptoms. Replacing it is a Gas Safe engineer’s job.
Is the pressure too low for the heating?
Some boilers will still manage hot water at low pressure but refuse to run the heating. Top up to 1 to 1.5 bar, and if it keeps falling, read why a boiler keeps losing pressure.
Has the pump failed?
The pump pushes hot water round the radiators. If it’s seized, the boiler may fire but the heat goes nowhere. Our guide to a boiler pump that isn’t working lists the warning signs.
Why does my system or regular boiler have hot water but no heating?
Is the heating zone valve stuck?
System and regular boilers use motorised valves to send hot water either to the cylinder or to the radiators. If the heating valve sticks shut, the cylinder still heats but the radiators don’t. You can sometimes see a manual lever on the valve head. An engineer can test it and swap the motor if needed.
Is there an airlock or a pump problem?
Air trapped in the pipework can stop water reaching the radiators. Bleeding the radiators may help, and our post on a boiler airlock explains what to do if it doesn’t.
Is the programmer or wiring centre at fault?
If the programmer shows heating on but nothing happens, the fault may be in the wiring centre that links the controls to the boiler. That’s one for an engineer.
| Symptom | Combi | System or regular |
|---|---|---|
| Boiler fires, radiators cold | Diverter valve or pump | Zone valve or pump |
| Boiler doesn’t fire for heating | Thermostat, timer or pressure | Thermostat, timer or wiring |
| Some radiators warm, others cold | Air or sludge | Air or sludge |
What if the heating comes on but the radiators stay cold?
If the boiler is clearly running for heating but the radiators aren’t warming, it’s more likely to be air, sludge or balancing. Our guide to radiators not heating up works through it. If the boiler won’t fire at all, see boiler not firing up.
When is it time for a new boiler?
If your boiler is over 8 years old and diverter or pump faults keep cropping up, replacement usually makes more sense than another repair. Those parts tend to wear out together on older boilers.
We fit replacement boilers from Worcester Bosch, Vaillant, Baxi and Ideal, with fixed prices. Long, market-leading warranties through Clever Energy help keep your new boiler protected for years. Find out more about our boiler replacement service.
Hot water but no heating FAQs
Why is my central heating not working when the hot water is fine?
It’s usually the thermostat or timer. If those are fine, a combi’s diverter valve or a system boiler’s zone valve is the likely culprit.
Can a thermostat stop the heating working?
Yes. Flat batteries, a lost wireless connection or a setting below room temperature will all stop the boiler firing for heating.
Does a diverter valve affect the heating?
Yes. On a combi, it controls whether hot water goes to the taps or the radiators, so a stuck valve can leave the heating cold.
Is no heating an emergency?
It can be for vulnerable people in cold weather. Use portable heaters in the meantime and get an engineer booked quickly.
