Common heating faults for Y and S plan layouts.

There are a wide range of common faults that occur on heating systems, some more specific to particular component manufacturers than others. You will need an electrical test meter to carry out these tests.

If you boiler has stopped completely then check the fuse to see if there's power going to the unit. If there is power then you need to check whether the controls that link to the boiler are 'on'.

Check that your programmer is set in the 'on' position. Check that the boiler is being sent a 'demand' signal, known as 'switched live', SWL for short. If this is present then the boiler should be firing up. If there is a fault light on the boiler check the manufacturers instructions to see if there's anything obvious to check. After that you should instruct a gas safe engineer to analyze the problem further.

If there's no SWL signal at the boiler then the fault lies in the control valves or thermostats controlling them.

For 'S' plan systems the 2 port brown wires should have demand for each function. If it doesn't then the problem is most likely to be the thermostat. If there is demand on the 2 port valve but no output then most likely the 2 port valve is faulty and needs to be replaced.

For Y plan systems check that the 3 port valve has a live signal on the gray wire when Hot water is 'off'. Then check that SWL goes live when you have hot water on and the cylinder thermostat requesting heat.

A common fault with 3 port valves is that the central heating comes on when the hot water only is selected and this is often because of incorrect wiring of the hot water off cable.