If your hot water works normally but the radiators stay cold, your boiler is clearly still producing heat. The problem may instead involve heating controls, radiator flow or the way the boiler directs heat to the central-heating circuit.
This symptom is useful because it narrows down the possibilities. Start with simple settings before assuming an internal boiler fault.
Some boilers can be set to provide hot water only. This is commonly used during warmer months when central heating is not needed.
Check the boiler display and heating controls to make sure central heating has not been disabled.
Make sure the thermostat is asking for heat. Set it above the current room temperature and wait for the heating system to respond.
Also check the timer schedule, day and time, smart thermostat app, holiday mode, wireless thermostat batteries and heating zones. Clock changes or power cuts can sometimes alter timer settings.
If only one or two radiators are cold, the problem may be local rather than the boiler. Check thermostatic radiator valves and feel for cold spots.
Cold at the top can suggest trapped air. Cold at the bottom can indicate sludge or restricted circulation.
See Radiators Not Heating Up? What Cold Spots Mean & What to Check for more detail.
If every radiator is cold, investigate controls, pressure and the wider heating circuit.
Low system pressure can prevent some boilers from operating the central heating correctly. Compare the pressure gauge with the manufacturer’s recommended range.
If pressure repeatedly falls, do not simply keep topping it up. The underlying cause should be investigated.
A combi boiler provides both hot water and central heating from one appliance. A diverter valve directs heat according to demand.
If the valve becomes stuck or fails, the boiler may continue to provide hot water while failing to send heat to the radiators. This is an internal boiler fault and should be diagnosed by a Gas Safe registered engineer.
Homes with a hot-water cylinder use a different arrangement. A motorised or zone valve can control whether heated water travels to the cylinder or the radiators.
If the valve fails in one position, hot water may work while central heating does not.
A heating system needs adequate circulation. A pump or flow problem can prevent hot water reaching radiators even while domestic hot water remains available.
Possible signs include radiators staying cold, unusual pump noises, some areas warming while others do not or the heating cutting out.
Confirm heating mode is enabled, raise the thermostat setting, check timer and smart-control schedules, check boiler pressure, note fault codes, check radiator TRVs and look for visible leaks.
Do not remove the boiler casing.
A single reset according to the manufacturer’s instructions may clear a temporary fault. Before resetting, make a note of any fault code.
If the same fault returns, repeated resets are not a repair.
Arrange professional diagnosis if all radiators remain cold, settings and thermostat appear correct, a fault code returns, boiler pressure is abnormal, you suspect a diverter valve or the boiler repeatedly shuts down.
TES Heating can diagnose central-heating and boiler faults across London.
The heating may be disabled, the thermostat may not be calling for heat, radiator flow may be restricted or an internal valve may not be directing heat correctly.
Yes. Low pressure can stop some boilers from running the heating circuit correctly.
Yes. Incorrect settings, flat batteries, wireless connection problems or a faulty thermostat can prevent the heating from being requested.
No. Diverter valves apply mainly to combi boilers. Other boiler types can use different motorised valves and controls.
If the fault involves internal gas-boiler components, professional diagnosis should be carried out by a Gas Safe registered engineer.
