You turn on the taps and get lovely hot water, but your radiators stay stone cold. It’s a common issue with combi and system boilers, especially during the colder months when your central heating system is in use. If you’re in this situation, don’t panic. The cause is often something simple and easily fixed.
At Heat IQ, we help homeowners get their heating running smoothly again with expert advice and professional service. Below, we’ll walk you through the most common reasons your hot water works but your heating doesn’t, and what you can do next.
Diverter Valve May Be Stuck
The diverter valve controls whether the hot water from your boiler is directed to your taps or radiators. If it’s stuck in the hot water position, your heating won’t get any warmth, even if the boiler is firing correctly.
This issue usually needs an engineer, as the valve is located inside the boiler. It is one of the most frequent faults we see with combi boilers.
Thermostat Might Not Be Responding
The room thermostat instructs the boiler when to activate the heating. If it’s faulty, incorrectly placed, or set too low, it may not send the proper signal. In some cases, wireless thermostats lose connection or run out of battery.
It’s worth checking:
- The thermostat is set above room temperature
- Batteries are working
- The settings or timer are programmed correctly
If you use a smart thermostat, check the app for any warnings or lost connections.
Boiler Pressure Could Be Too Low
If your boiler pressure is below 1 bar, it may not circulate water through the central heating system. Most boilers operate best between 1 and 1.5 bar when cold. Low pressure can happen due to a leak, recent radiator bleeding, or natural loss over time.
Check the pressure gauge on the front of your boiler. If it’s low, your system might need topping up. Always consult your manual first or call Heat IQ for guidance if you’re unsure.
Airlocks Might Be Blocking Flow
Air trapped in the pipes or radiators can stop hot water from flowing properly. This often affects one or two radiators, but in some cases, it can disrupt the whole heating system.
Bleeding the radiators is usually enough to release trapped air. Use a radiator key, turn slowly, and have a cloth ready to catch drips. If this doesn’t help, there may be an airlock in the pipes that needs professional attention.
Heating Settings Might Be Wrong
Sometimes, the issue comes down to a control setting. If your boiler is in ‘hot water only’ mode or the heating programme is off, the boiler will ignore your heating schedule.
Check:
- The heating mode is switched on
- The programmer is set to the correct time
- The thermostat is not on holiday or frost setting
Simple checks like these can resolve the issue without requiring any specialised tools or technical knowledge.
Other Causes That Could Be Involved
Other parts might be at fault, including:
- A faulty circulation pump
- Zone valve issues in larger or older systems
- Sludge or debris build-up inside radiators or pipework
These usually require professional diagnostics. Heat IQ engineers carry specialised tools to inspect all key components and provide guidance on the most cost-effective repair options.
Checks You Can Try Yourself
Before booking a boiler repair, there are a few safe checks you can carry out at home.
| Check | What To Look For | What You Can Do |
|---|---|---|
| Thermostat | Low setting or dead batteries | Turn it up and replace batteries |
| Pressure Gauge | Below 1 bar | Top up if safe to do so |
| Radiators | Cold at the top | Bleed with radiator key |
| Boiler Controls | Hot water only mode or timer off | Reset to heating mode |
| Heating Schedule | Timer set incorrectly | Adjust time and programme |
Heat IQ for Boiler Repairs
There’s no need to struggle with a chilly home. Our qualified engineers at Heat IQ are trained to diagnose heating problems quickly and get your system running correctly again. Whether it’s a diverter valve, thermostat, or internal part, we’ll sort it with transparent pricing and friendly service.
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