Central heating 3 way valve. Advice required please.

[B16 RFF]

I have a fully pumped system with a Honeywell V4073A 3 way valve controlling the flow to the hot water cylinder and the central heating. The problem I have is that the pump and boiler will not run unless the hot water side is calling for heat, no matter what I do to the central heating side. An ex-plumber friend has suggested the 3 way valve could be at fault. I have removed the cover of the valve's power head, and the motor is very hot (although valve body is cold), leading me to think something has jammed and the motor is overheating. I am able to move the lever from auto to open and back.
There seems to be very little rotation on the spindle of the actual valve, 45 deg or less. Is this correct, or is there a fault on the valve?

Thanks,

Paul.

[B16 RFF]

Thanks for your replies. I have bitten the bullet and replaced the actuator unit, and all seems to be ok now. On closer examination of the old unit, it looks like one of the microswitches is faulty.

Cheers,

Paul.