Central Heating Not Working but Hot Water Is? Safe Checks
By Adrian Plumbing & Heating Ltd
In short
When hot water works but radiators stay cold, the cause is often a control, setting or component issue rather than the boiler itself. Safe checks are limited to user controls such as the programmer, thermostat and valves. If you smell gas or suspect carbon monoxide, get to fresh air and call the National Gas Emergency Service on 0800 111 999 from outside.
On this page
Gas safety first
Before any troubleshooting, know what to do in a gas emergency. If you smell gas or suspect carbon monoxide, do not operate any switches, lights or flames. Leave the property, get to fresh air, and call the National Gas Emergency Service on 0800 111 999 from outside the building. If there is immediate danger, contact the emergency services. These steps take priority over any heating fault.
Match the symptom to the next step
The pattern of which radiators are cold can narrow down where to look. Use this table to understand what each symptom commonly suggests. Component faults listed here are possibilities that need professional diagnosis, not conclusions.
Swipe or scroll to compare →| Symptom | What it may suggest | Safe next step |
|---|---|---|
| Every radiator cold, hot water works | Heating may be off at a control, or a component such as a pump or diverter valve is not directing heat to the radiators. | Check the programmer and thermostat are set for heating, not hot water only. |
| One radiator cold, others warm | A single valve may be closed or stuck, or that radiator needs balancing or bleeding. | Check the TRV setting on that radiator. |
| Radiators partly warm | System may need balancing, or there may be a circulation or sludge issue. | Note the pattern and ask an engineer to assess. |
| Radiators cold at the bottom, warm at top | Possible sludge or restricted flow in that radiator. | See our guide on a radiator cold at the bottom. |
| Radiator cold all over | Valve may be closed, or the radiator is not receiving flow. | Check the valves are open and contact an engineer if unchanged. |
Safe checks you can make
Only checks that use the external controls are safe for a homeowner to make. Never open the boiler casing, attempt to repair a diverter valve, pump or wiring, loosen unknown valves, or repeatedly reset the boiler. The following are limited to user-level controls:
- Heating enabled: confirm the programmer is set to heating, not summer or hot-water-only mode. It is easy to switch heating off during warm weather and forget to turn it back on.
- Time and schedule: check the programmer time and heating schedule are correct. A power cut can reset clocks and upset timers.
- Thermostat demand: turn the room thermostat up above the current room temperature and listen for a click. If the display is blank, check or replace the batteries following the manual.
- TRV settings: check thermostatic radiator valves are not turned down or off on the radiators you want to heat.
- Display and fault codes: note any fault code or warning shown on the boiler display. Write it down for the engineer.
- Pressure: compare the visible pressure reading against the range stated in your model's manual. Many systems sit around 1 to 1.5 bar when cold, but the manual is authoritative.
If pressure is dropping repeatedly, read our guide on boiler pressure that keeps dropping before repressurising, and only follow the exact steps in your manufacturer's manual.
Before you call an engineer
Gathering a few details first helps an engineer diagnose the fault more quickly. Before you call, note:
- Boiler make, model and any fault code on the display.
- Which radiators are cold and which are warm.
- Whether hot water is working normally.
- Any recent changes to controls, settings or power cuts.
- The pressure reading and the range stated in your manual.
With those details to hand, Adrian can help with boiler and heating repairs and talk through what you have found. Request a callback to arrange a visit at your Grays or South Ockendon home.
Disclaimer: This article provides general guidance only. Always follow your appliance manufacturer's instructions and use an appropriately qualified professional for gas, electrical and plumbing work. Gas work must be carried out by a Gas Safe registered engineer.
Frequently asked questions
Why does my hot water work but my heating does not?
It is often a control or setting issue, such as the programmer being in hot-water-only mode, or a component like a diverter valve or pump not sending heat to the radiators. Safe checks are limited to the external controls; diagnosing a component fault needs a qualified engineer.
Is it safe to reset my boiler if the heating stops?
A single reset following your manufacturer's instructions is generally fine, but repeatedly resetting a boiler that keeps locking out is not a fix. Note any fault code and contact an engineer if the problem returns.
Could low pressure stop my radiators heating?
Low pressure can affect heating performance, but the correct range is model-specific. Check your manual for the stated range and never remove the boiler casing to investigate. If pressure keeps dropping, ask an engineer to find the cause rather than repeatedly topping up.
