Are your radiators heating up when your system is switched to hot water only?

This is a common problem which not only leaves you very hot, but is a waste of our (now very expensive!) gas.

This fault can have a variety of causes. Whether you have a combination or a conventional boiler (with a separate hot water cylinder) there is a valve or valves which switch between hot water and heating. So why is this valve open to let your heating work?

You might have a faulty time-clock or programmer. This is not very common, but we do often find that these are set incorrectly – sometime set 12 hours out so midnight becomes midday. Check this.

Turn the hot water on, the heating off, and the room thermostat fully down (sometimes these are combined with the programmer) and see whether the heating goes off. If it stays on, you have identified that the fault is with the valve. If not, it’s usually the programmer.

In a combination boiler the diverter valve is usually at fault, although it can be caused by a faulty printed circuit board, giving out an incorrect signal.

In a conventional system there are sometimes 2 valves (2 port valves) and sometimes one (a 3 port valve). We frequently see one of the 2 port valves jammed open. In this position, they can send power to turn the boiler on. At the same time, although less frequently, both 2 and 3 port valves can simply jam and allow hot water into the heating system when the hot water is switched-on.

Having ascertained that the fault is with the valve (and which valve if there are 2) it is usually a job for a professional. Even more so, if the boiler is a combination boiler, it would be very unwise to try changing it yourself.


Taskforce Heating and Plumbing - Heating always on when the water is on - Hampshire and West Sussex

Based in Emsworth near Havant we cover southern parts of Hampshire and West Sussex. Get in touch here, or call us on 01243 370880.