No hot water but the heating works: what that combination means
If radiators get hot and taps do not, the burner, gas supply and pump are all working. That single observation rules out most of the boiler and points straight at the hot water path.
The engineering behind heating without hot water
On a combi the usual suspects are a stuck diverter valve, a scaled plate heat exchanger, or a failed flow turbine that never tells the boiler a tap has opened. On a stored hot water system it is normally the cylinder thermostat, the hot water zone valve, or a programmer channel that has failed. The diagnostic split is quick and tells you the likely cost within minutes.
Things worth knowing about heating without hot water
- Combi: diverter valve, plate exchanger or flow sensor
- Cylinder: zone valve, cylinder stat or programmer channel
- Lukewarm rather than cold usually means scale, not a valve
- Check the immersion heater as a temporary fallback if fitted
- Hot water only faults rarely need a new boiler
Scope of work
- Domestic boiler installation
- Boiler servicing
- Boiler maintenance and repair
Questions we get asked
- Why is the water lukewarm rather than cold?
- That pattern fits a scaled plate exchanger or a partially stuck diverter, where some heat still transfers.
- Can I use the immersion in the meantime?
- If your cylinder has one and it is in working order, yes — it is more expensive to run but keeps hot water available.
Where we deal with this
Related help pages
- Fan speed mismatchBaxi E168: fan speed fault on newer Baxi appliances
- Flue symptom guideSmoke from an oil boiler flue: colour, timing and what to do
- Worcester fault codeWorcester Bosch EA fault code: flame loss and ignition lockout
- Discharge faultWater dripping from the outside pipe: pressure relief valve discharge
- Oil boiler partsOil boiler fuel filters: the cheap part that prevents expensive faults
- Vacant property careServicing a boiler in an empty or unoccupied property
Services that cover this
Talk to us about heating without hot water
Put simply: Tell us whether the radiators are hot when you call. It narrows the fault before we arrive and shortens the visit.
Include the appliance make and model in your enquiry so the correct technical information can be checked.
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