BoilerBuddy · homeowner guide
No hot water, but the heating still works
Working radiators with cold hot-water taps is a different clue from a boiler that has stopped altogether. On some homes the hot-water controls or cylinder are separate from the room-heating controls; a boiler fault is possible too.
Similar symptoms can have different explanations. The possibilities below are not a diagnosis.
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Understand the symptom
What might be behind it?
A hot-water schedule or user control may be off even while the heating programme is on.
On a home with a hot-water cylinder, its controls and the boiler’s heating controls may behave separately.
A boiler or hot-water-system component may need professional attention. The symptom does not identify a particular valve or heat exchanger.
Safe observations
Checks you can make without opening the boiler
- 1
Confirm that more than one hot tap is affected and that the radiators still warm when their normal control calls for heat.
- 2
Check the visible hot-water schedule and user controls; use their instructions rather than changing installer settings.
- 3
Record any boiler display message or code without opening the case. Note whether the hot water fails immediately or changes after a short time.
Know when to stop
Stop if you notice
- A smell of gas, or a yellow, orange or sooty flame.
- A carbon monoxide alarm is sounding, or someone has possible CO symptoms.
- Smoke, scorching, visible damage, overheating or a leak around the boiler.
- The boiler keeps locking out or will not stay lit.
What not to touch
Do not open a cylinder cupboard to work on controls or pipework, remove the boiler casing, or attempt valve, electrical or gas repairs. Do not repeatedly reset the boiler.
When to contact a Gas Safe engineer
Ask a Gas Safe engineer to assess a persistent loss of hot water, especially if the display shows a fault or the heating begins to stop as well.
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Get help that matches what you can see
If you do not know the fault code or exact model, start with the symptom check. Record any displayed code from the screen without opening the boiler casing.
Official safety sources
HSE guidance says not to use an appliance you suspect is unsafe and that domestic gas work must be carried out by a Gas Safe registered engineer. Follow the emergency guidance if you suspect a gas leak or carbon monoxide exposure.
Fault-code guides for exact boiler models
Need a qualified engineer?
BoilerBuddy can pass what you've worked out to a local Gas Safe engineer — symptoms, checks, and the bits that point to the likely cause.
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Engineer handover
Send this sheet with you to the visit.
Print or email it to your engineer so they arrive already knowing what your boiler is doing and what you've already tried.