I have an old Ideal W boiler (conventional) which heats the water cylinder and will go to central heating only by selection .
Does the central heating operate only by having the water pump (Grundfos Selectric UPS 15-50) or does it need also a Diverter Valve. I have been tearing the floor up but cannot find a valve.

Tony Donnarumma, September 2014

In some old style systems the water tank was heated by gravity ( a throw back from the back boiler fireplace) the c/heating by a pump,one way to test is to put the programmer on to "hot water only" in gravity fed systems the pump does not run but the boiler does

toptrish, September 2014

I think that there will be a 3 port mid position valve (diverter) but I can't imagine it being fitted under the floor.

The valve directs the heated water either to the cylinder or to the radiators or both - as required. The pump just continuously circulates the heated water - as directed by the diverter valve - as far as I know.

Follow the route of the hot water outflow from your boiler - or the control wires that run to it - they will eventually take you to the valve - I think they usually put the valve close to the hot cylinder.

I am not qualified to answer you with any confidence.

Good luck...

I K Brunel, September 2014