Mid-Position Valve

[jbmc]

Is it normal for the orange wire of the mid position valve to temporarily cease being live when the valve is switching from the mid-position (heating + h/w) to the heating only position? This causes the boiler to momentarily turn off.

 

[HootingOwl]

What is the make of the 3 port?

 

[jbmc]

It's the Honeywell V4073A.

 

[stem]

Is it normal for the orange wire of the mid position valve to temporarily cease being live when the valve is switching from the mid-position (heating + h/w) to the heating only position? This causes the boiler to momentarily turn off.

Perfectly normal. In the hot water only, or hot water and heating positions, the boiler is controlled by the thermostat on the hot water cylinder. When the hot water is up to the correct temperature, the cylinder thermostat turns off the boiler. At this point, if the central heating is still required, the valve's motor will start to wind over to the heating only position. In doing so, it operates a microswitch which energises the orange wire to take over the boiler control.

The small delay in the valve moving from central position, to the heating only position and triggering the microswitch causes the 'blip' you describe.