Hot Water But No Central Heating

A boiler that seems to be working with hot water supply still pouring out of the tap but no central heating? Your central heating insurance will help out in circumstances as this. You have one of two possible types of scenario: boiler settings and central heating system settings or two, the components of the boiler – more specifically the motorised diverter valve – have decided to stop working.


For central heating issues, check all the radiators first. If just one radiator has a satisfying, even warm touch, then there is no need to worry about the boiler

A less warm radiator would be worth bleeding for air and water. With the special key, turn the bleed valve on the side of the radiator in an anti-clockwise motion. Put some bowels and towels underneath to prevent dirty water from staining the carpet or wood.

However, radiators that have a chilly bottom while warmer at the top are probably full of sludge; cleaning a radiator is a more time-consuming and difficult endeavour.

No luck? If you have good reasons for suspecting your radiators, read some further guides.


Central heating settings (Checking Timers)

First of all, are all thermostats dialled up to the correct temperatures? Are timers set to the present time period that you would like heat for (check 24-hour or 12-hour clock)?

A recent power outage may have reset the boiler. Using the manual, walkthrough, and soft-reset the settings again. If the clocks have recently changed because of Daylight Savings, then your timer may need to be adjusted too.

The timer may have been affected by the clocks changing too or back-up batteries failing or even somebody altering the settings without your knowledge.

It should be straightforward to see at the timer control panel if the boiler is currently active for hot water. If you are not sure, check your timer manual.

Boiler problems

Boiler pressure: Is at one bar? Good. If the water pressure is low, then your central heating may fail to do what it needs to optimally. If the pressure is below one bar, then it is time to repressurise the boiler. It may be necessary to read the manufacturer’s notes for this too.

A soft reset could work. There may be a reset button or switch on the outside of the appliance. Do not take off a boiler cover or any casing, as this can potentially be life-endangering. You can also try turning off the electricity to the boiler, waiting 60 seconds, and then turning it on once again.

Faulty diverter valves

If all else has failed, then the issue may be a diverter valve that has stopped working.

These valves switch between heating water and heating radiators.

They can be found in nearly all combi boiler systems, with the aim of controlling the flow of water through the radiators, taps, and showerheads. A combi boiler will prioritise the flow of water in a home water system depending on what is currently being used.

Usual wear and tear can lead to these valves from being unable to change position and with it, either central heating or hot water will stop. For example, when the heating is turned on, the boiler will run, the pump turns on and the diverter valve sends heat to the radiators. In a usual working boiler, if the hot tap is turned on, the pump begins working, heating the boiler, and the primary pipes from the pump start working too. The fan runs, air switch activates, and the diverter valve keeps heat within the boiler. The pump sends heat around the boiler and hot water heat exchanger. Any cold water flowing through this hot water heat exchanger keeps fresh clean, cold water apart from dirtier boiler water. The end result is hot water at your taps but also heat to your radiators.

It is worth getting a few quotes on the replacement of a diverter valve.

A diverter valve/switch replacement should be around £75-£100 depending on the engineers’ rates. We recommend that if you need your boiler serviced to get it done at the same time and save some money!